Multicolor serial dot printer
This application is a continuation of application Ser. No. 716,510 filed Mar. 25, 1985, now abandoned, which was a continuation of Appln. Ser. No. 442,361, filed Nov. 17, 1982, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multicolor serial dot printer and, more particularly, to a multicolor serial dot printer which is simple in construction, allows multicolor printing and printing which is easy to recognize, and economizes on printing paper sheets. 
     2. Description of the Prior Art 
     In a conventional multicolor serial dot printer, memories for storing printing data have some difficulties in configuration, moreover, it is hard to control fetch of the memory contents and requires an increased number of program steps. 
     The conventional multicolor serial dot printer is also unsatisfactory in easy recognition of printed data, especially of graph data. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to solve the problems described above. 
     It is another object of the present invention to provide a printer having memories of which number is corresponding to that of printing colors. 
     It is still another object of the present invention to provide a printer which allows easy recognition of graph and other printed data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing an example of arrangement of a keyboard in a calculator with a printer according to the first embodiment of the present invention; 
     FIG. 2 is a block diagram showing the overall configuration of the first embodiment of the present invention; 
     FIG. 3 is a view showing a dot configuration of a graph printed by the first embodiment of the present invention; 
     FIGS. 4(A) and 4(B) are views showing examples of dot configuration of individual characters printed by the first embodiment of the present invention; 
     FIGS. 5A to 5C are views showing examples of contents of printing memories in the first embodiment of the present invention; 
     FIG. 6 is a view showing an example of data printed by the first embodiment of the present invention; 
     FIG. 7 is a plan view showing an example of a keyboard utilized in a device with a printer according to the second embodiment of the present invention; 
     FIG. 8 is a block diagram showing overall configuration of the second embodiment of the present invention; 
     FIG. 9 is a view showing the dot configuration of a graph printed by the second embodiment of the present invention; 
     FIGS. 10(A) to 10(C) are views showing examples of dot configuration of individual characters printed by the second embodiment of the present invention; 
     FIGS. 11A to 11E are views showing examples of contents of printing memories in the second embodiment of the present invention; and 
     FIG. 12 is a view showing an example of data printed by the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a keyboard of a calculator having a dot printer according to the first embodiment of the present invention. A keyboard KB has a slide switch SW1 for selecting either the normal printing mode and the graph printing mode, in addition to numeral keys NK and function keys FK. 
     FIG. 2 is a block diagram of the first embodiment of the present invention. The calculator basically has a control section CC for controlling the overall system, printing memories PCM1 and PCM2 for storing printing data, and a printer control section PCC for controlling the printer. The printer is a serial dot printer which has ink jet nozzles for printing in black and red, respectively, which are mounted horizontally, on a carriage driven by a linear motor. A driver circuit PZD drives piezoelectric elements constituting the ink jet nozzles. The piezoelectric elements corresponding to black and red, respectively, are driven through signal lines l B1  and l R1 , and black and red ink are injected from the nozzles. 
     When the slide switch SW1 of the keyboard KB in FIG. 1 is switched from the normal printing mode to the graph printing mode, the control section CC detects this through a signal line l S . Then, the function keys FK on the keyboard KB are prepared for graph data input. The graph is performed by groups of dots. Each line of the graph comprises a matrix of 126×7 dots, as shown in FIG. 3. Each of the printing memories PCM1 and PCM2 in FIG. 2 has a capacity of 126 bytes, each byte comprising 8 bits corresponding to 1×7 dots of the line data. The printing memory PCM1 is assigned for printing in black, while the printing memory PCM2 is assigned for printing in red, thereby allowing printing in black and red. 
     In order to print a graph which represents both target values and actual obtained values, designating 500 as a maximum value of a scale, the numeral 500 is input through the keyboard KB; a function key FK for modifying the input data as a scale numeral on the scale, such as a key , is depressed; and then, the control section CC judges first that the input data is to be printed as the scale numeral. Dot patterns representing the input numeral 500, the numeral 250 obtained by dividing it by two, and the numeral 0 are stored in the printing memory PCM1 together with dot patterns representing spaces. Dot patterns representing spaces are stored in the printing memory PCM2. These operations are performed in the following manner. Firstly, the numeral 125 is set in a printing dot register PR through a signal line l PR . A printing dot counter PC and a line counter LC are cleared through a signal line l C . An output signal line l AD  of the dot counter PC is an address signal line for the printing memories PCM1 and PCM2. A signal line l A1  is set to logic level &#34;1&#34; to open an AND gate AD1 so that printing data on a data signal line DB1 may appear on a signal line DB2. This printing data is stored in the printing memory PCM1 by setting a read/write signal line l RW1  for black to logic level &#34;0&#34;. The contents of the printing dot register PR and the printing dot counter PC are compared. If they do not coincide, the count of the dot counter PC is incremented by one through a signal line l PC , and the next printing data of 7 dots is stored in the printing memory PCM1. This operation is repeated until the contents of the printing dot counter PC and the printing dot register PR coincide, thereby storing the graph data of 126 bytes. 
     Meanwhile, 126-byte printing data of logic level &#34;0&#34;, that is, the dot patterns representing spaces, are also stored in the printing memory PCM2 by setting a signal line l A2  to logic level &#34;0&#34; to close an AND gate AD2 and by setting a read/write signal line l RW2  for red to logic level &#34;0&#34;. 
     The printing data is stored in the printing memories PCM1 and PCM2 in units of bytes, each byte comprising 8 bits corresponding to printing data of 1×7 dots. The printing data is dot pattern data generated by a character generator CG in the control section CC. Each dot pattern of 1×7 dots is expressed in hexadecimal notation. Illustrating a numeral &#34;7&#34; and a staggered pattern as shown in FIG. 3, the numeral &#34;7&#34; is represented by &#34;C0&#34;, &#34;A0&#34;, &#34;90&#34;, &#34;8E&#34; and &#34;C0&#34; from the right in hexadecimal notation as shown in FIG. 4(A), while the staggered pattern is represented by &#34;D6&#34;, &#34;AA&#34;, &#34;D6&#34;, &#34;AA&#34;, and &#34;D6&#34; as shown in FIG. 4(B). In FIGS. 4(A) and 4(B) , black circles represent dots printed in black, while hatched circles indicate dots printed in red. 
     In the case of scale numerals under discussion, data of numerals 500, 250 and 0 is printed. The contents of the printing memories PCM1 and PCM2 have formats as shown in FIG. 5A. The printing data stored in the printing memories PCM1 and PCM2 is transferred to the printer control section PCC and the printer is operated to perform printing. 
     The mode of operation will now be described with reference to FIG. 3. In the first embodiment, the printer is an ink jet printer wherein paper feed is performed by a pulse motor PM, ink jet nozzles of the on-demand type for printing in black and red are horizontally mounted on a carriage which is driven by a linear motor LM, and the piezo driver circuit PZD is driven by a timing pulse TP generated by a carriage position sensor FDP during reciprocative movement of the carriage. 
     When the printing data is stored in the printing memories PCM1 and PCM2 in this manner, the control section CC clears the printing dot counter PC and the line counter LC to initialize the addresses of the printing memories PCM1 and PCM2 by setting the signal line l C  to logic level &#34;0&#34;. After setting the black and red read/write signal lines l RW1  and l RW2  logic level &#34;1&#34; (read state) and confirming that a busy signal line l Bsy  from the printer control section PCC is at logic level &#34;1&#34; (not in the busy state), the control section CC sets a signal line l PF  to logic level &#34;1&#34; and a signal line l PB  to logic level &#34;0&#34; so as to instruct the printer control section PCC to start printing. Then, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34; (busy state), sets a drive signal line l F  of the linear motor LM to logic level &#34;1&#34;, and sets a drive signal line l B  to logic level &#34;0&#34; so as to drive the carriage toward the left from its home position (right-hand position on a printing paper sheet P). During this time period, the timing pulses TP from the carriage position sensor FDP are detected. In response to the timing pulse immediately next to that corresponding to the printing start position, the printer control section PCC sets the signal line l Bsy  to logic level &#34;1&#34; so as to signal to the control section CC that the printing data may be transmitted. In response to this, the control section CC sets a signal line l REQ  to logic level &#34;0&#34; to signal to the printer control section PCC that the data on data lines D p1  and D p2  is valid. Then, the printer control section PCC sets the signal line l Bsy  to logic level &#34;0&#34; (busy state) to read the printing data from the printing memories PCM1 and PCM2. In response to the next timing pulse TP, the piezo driver circuit PZD is driven through the signal lines l B1  and l R1  to print in black and red in accordance with the state of the most significant bit of the first byte of 1×7 dots. Since the printing data is &#34;00&#34; for black and red as shown in FIG. 5A, a space is printed. When this printing is completed, the printer control section PCC sets the signal line l Bsy  to logic level &#34;1&#34; to signal to the control section CC that the next printing data may be transmitted. Then, the control section CC increments the printing dot counter PC by one through the signal line l PC , and then increments the addresses of the printing memories by one. The next printing data is supplied to the data signal lines D P1  and D P2 . The control section CC sets the signal line l REQ  to logic level &#34;0&#34; to indicate that the data on the data signal lines D P1  and D P2  is valid. The printer control section PCC reads the data from the printing memories PCM1 and PCM2 and performs printing in response to the next timing pulse. 
     In this manner, the data of the most significant bit of each byte of 1×7 dots of black and red printing data (first row of one 126×7 dot matrix) shown in FIG. 5A is printed to the left. During this time period, a coincidence circuit CO monitors coincidence between the contents of the printing dot counter PC which is incremented by one upon every printing operation and of the printing dot register PR. When coincidence occurs, the control section CC detects completion of printing of first 126 dots, clears the contents of the printing dot register PR through the signal line l PR , and sets the signal lines l PF  and l PB  to logic levels &#34;0&#34; and &#34;1&#34;, respectively. 
     Subsequently, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34;, and the drive signal lines l F  and l B  to logic levels &#34;0&#34; and &#34;1&#34;, respectively so as to drive the carriage to the right and to start printing to the right. The pulse motor PM is driven to feed the printing paper sheet by one dot pitch. As in the case of printing to the left, in response to the timing pulse immediately next to that corresponding to the printing start position, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;1&#34; to signal to the control section CC that the printing data may be transmitted. The control section CC then sets the signal line l REQ  to logic level &#34;0&#34; to indicate that the initial data for printing the second row of the 126×7 dot matrix to the right, that is, the 126th dot, is valid. Then, the printer control section PCC receives the printing data and executes printing in response to the next timing pulse TP. Thereafter, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;1&#34; to indicate that the next printing data may be transmitted. Since the next printing must be performed to the right-hand side, the control section CC decrements by one the count of the printing dot counter PC to thereby decrement the printing memory addresses by one through a signal line l BC . The control section CC transfers the data of the 125th dot to the data lines D P1  and D P2 , sets the signal line l REQ  to logic level &#34;0&#34;, and performs printing in response to the next timing pulse TP. In this manner, the second row of the 126×7 dot matrix of black and red printing data is printed to the right. As in the case of printing the first row, when the coincidence of the printed dot number with 126 dots is detected by the coincidence circuit CO, the control circuit CC increments by one the count of the line counter LC through a signal line l 1 . An output signal line l 2  of the line counter LC is for detecting if four reciprocative printing operations of the carriage have been completed, that is, if one line has been printed. Since only one reciprocative movement has been completed in this case, no output is produced from the output signal line l 2  in this case. The control section CC sets the printing dot register PR to 125, and sets the signal lines l PF  and l PB  to logic levels &#34;1&#34; and &#34;0&#34; to instruct printing of the third row of the 126×7 dot matrix. In response to this, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34; to perform paper feed of one dot pitch and sets the drive signal lines l F  and l B  of the linear motor LM to logic levels &#34;1&#34; and &#34;0&#34; to perform printing to the left. The printing direction is reversed when the coincidence circuit CO detects another coincidence of the printed dot number with 126 dots. In this manner, four reciprocative movements of the carriage, that is, printing of one line, are completed. When printing of one line is completed, the control section CC receives an output from the output signal line l 2  of the line counter LC to thereby detect that the 126×7 dot matrix, or one line, is completed. 
     Since the scale numerals have been printed, the control section CC, referring to a signal line l FD , instructs the printer control section PCC, through a signal line l FD , to perform the paper feed of one dot pitch. In response to this, the printer control section PCC performs paper feed of one dot pitch. Subsequently, the control section CC stores the data of the scale lines to the printing memories PCM1 and PCM2, as shown in FIG. 5B. Since printing of the scale lines involves only printing in black, data of logic level &#34;0&#34; is stored in the printing memory PCM2 corresponding to printing in red. In the same manner as printing of the scale numerals, printing of the contents in the printing memory PCM1 corresponding to printing in black is executed by four reciprocative movements of the carriage, thus completing scale printing instructed by input through the keys  5,  ,  0,  ,  0,  ,   . 
     The graph printing data is then input by, for example, the keys  4,  ,  0 ,  0 , and  +  as a target value, and keys  3 ,  0 ,  0 ,  + , and    as an actually obtained value. Then, the control section CC recognizes that graph printing is to be performed and calculates the printing position of a bar for the input numeral 400 reference to the maximum scale numeral 500.  In this case, as shown in FIG. 3, the maximum scale numeral 500 corresponds to the 100th dot (from the scale numeral 0 in the direction toward the right) and 400 therefore corresponds to the 80th dot from the scale numeral 0. Therefore, the printing position of the bar for 400 within the 126-dot row is the 32nd dot after 31 spaces from the right-hand side of the printing paper sheet P. The numeral 100 obtained by subtracting the actually obtained numeral 300 from the target value 400 corresponds to a width of 20 dots, and this portion is printed in a different pattern than is the bar portion of the actually obtained numeral 300. This portion corresponding to 100 dots is printed in red and hollow, while the bar portion corresponding to the actual obtained value 300 (60 dots) is also printed in red but in a staggered pattern. The corresponding printing data is stored in the printing memory PCM2. 
     The percentage 75% obtained by dividing the actually obtained value 300 by the target value 400 is to be printed in black and the data on this is stored in the printing memory PCM1 for printing in black together with a two-digit item 01. These pieces of data are stored in the printing memory PCM1 such that the percentage 75% and the item 01 may be printed at suitable positions with spaces therebetween. In this embodiment, the symbol &#34;%&#34; is stored from the 90th dot after 89 dots from the right-hand side, and the subsequent data is stored in the order of one space, numeral 5, one space, numeral 7, five spaces, one scale line (corresponding to zero), two spaces, numeral 1, two spaces, numeral 0, and two spaces, as shown in FIG. 5C. 
     When the graph data is stored in the printing memories PCM1 and PCM2, the control section CC performs four reciprocative movements of the carriage in the same manner as in printing the scale numerals so as to perform graph printing. As described above, the data on the percentage 75%, the scale lines and the item 01 are stored in the printing memory PCM1 for printing in black, while data on the staggered pattern of the actually obtained value and the hollow pattern of the difference between the reference value and the actually obtained value is stored in the printing memory PCM2 for printing in red. Since printing is performed at the same positions within the 126×7 dot matrix, printing of the graph and the data superposed on each other as shown in FIG. 3 may be performed. The item 01 in FIG. 6 shows the printed state. 
     In a similar manner, the keys  2 ,  0 ,  0 , and  +  as a target value, and the keys  1 ,  0 ,  0 ,  + , and    as an actually obtained value are input to perform printing of item 02 shown in FIG. 6. The keys  3 ,  0 , 0 , and  +  as a target value and the keys  2 ,  5 ,  0 ,  + , and    as an actually obtained value are input to perform printing of item 03 shown in FIG. 6. The numbers of these items 01 to 03 are produced by the counter inside the control section CC. 
     According to this embodiment, since the data necessary for understanding of a graph, such as numeral data, may be printed superposed on the graph, which has a staggered pattern, visual recognition of the graph and accompanying data on a narrow printing paper sheet P may be facilitated. This also results in economizes in the number of printing paper sheets required. 
     FIGS. 7 to 12 show the second embodiment of the present invention. 
     Referring to FIGS. 7 and 8, when a print mode switch SW2 on a keyboard KB is switched from the normal printing mode to the graph printing mode, a control section CC detects that the printing mode has been switched to the graph mode through a signal line l S . Then, the function keys on the keyboard KB are switched for graph data input. Graph printing is performed by groups of dots. Each printing line comprises a matrix of 126×7 dots, as shown in FIG. 9. Each of the printing memories PCM1 and PCM2 in FIG. 8 has a capacity of 126 bytes, each byte comprising 8 bits corresponding to printing data of 1×7 dots. The printing memory PCM1 is assigned for printing in black, while the printing memory PCM2 is assigned for printing in red, thereby allowing printing in black and red. 
     The keys  0  and   , the keys  5 ,  0 ,  + , and   , and the keys  5 ,  0 ,  - , and    are depressed to input a target value of 0, a maximum positive numeral of 50, a maximum negative numeral of -50, and the graph data printing mode instruction, respectively. Then, the control section CC recognizes from the first three data inputs after the switching operation of the printing mode switch SW2 that the current mode is the scale numeral printing mode. The control section CC stores together with data of spaces the dot patterns representing the above input data to predetermined addresses of the printing memory PCM1. The control section CC also stores the dot patterns representing spaces in the printing memory PCM2. 
     The above operation is performed in the following manner. Firstly, the numeral 125 is set in a printing dot register PR through a signal line l PR . A printing dot counter PC and a line counter LC are cleared through a signal line l C . An output signal line l AD  of the dot counter PC is an address signal line for the printing memories PCM1 and PCM2. A signal line l A1  is set to logic level &#34;1&#34; to turn on an AND gate AD1 so that printing data on a data signal line DB1 may appear on a signal line DB2. This printing data is stored in the printing memory PCM1 by setting a black read/write signal line l RW1  to logic level &#34;0&#34;. The contents of the printing dot register PR and the printing dot counter PC are compared. If they do not coincide, the count of the dot counter PC is incremented by one through a signal line l PC , and the next 1-byte printing data of 1×7 dots is stored in the printing memory PCM1. This operation is repeated until the contents of the printing dot counter PC and the printing dot register PR coincide, thereby storing the graph data of 126 bytes. 
     Meanwhile, 126-byte printing data of logic level &#34;0&#34;, that is, the dot patterns representing spaces, is also stored in the printing memory PCM2 by setting a signal line l A2  to logic level &#34;0&#34; to turn off an AND gate AD2 and by setting a red read/write signal line l RW2  to logic level &#34;0&#34;. 
     The printing data is stored in the printing memories PCM1 and PCM2 in units of bytes, each byte comprising 8 bits corresponding to printing data of 1×7 dots. The printing data is dot pattern data generated by a character generator CG in the control section CC. Each dot pattern of 1×7 dots is expressed in hexadecimal notation. Taking the numeral 5 and a staggered pattern of a scale line &#34;  &#34; as shown in FIG. 9, the numeral 5 is represented by &#34;8C&#34;, &#34;92&#34;, &#34;92&#34;, &#34;92&#34; and &#34;F4&#34; from the right in hexadecimal notation as shown in FIG. 10(A), while the staggered pattern &#34;  &#34; is represented by &#34;E0&#34;, &#34;80&#34;, &#34;80&#34;, &#34;80&#34;, and &#34;80&#34; as shown in FIG. 10(B). In FIGS. 10(A) and 10(B), black circles represent dots printed in black, while hatched circles represent dots printed in red. 
     In the case under discussion of printing scale numerals, data of numerals -50, 0 and 50 is printed. The contents of the printing memories PCM1 and PCM2 have formats as shown in FIG. 11A. The printing data stored in the printing memories PCM1 and PCM2 is transferred to the printer control section PCC and the printer is operated to perform printing. 
     The mode of operation will now be described with reference to FIG. 9. In the second embodiment, the printer is an ink jet printer wherein paper feed is performed by a pulse motor PM, ink jet nozzles of the on-demand type for printing in black and red are horizontally mounted on a carriage driven by a linear motor LM, and the driver circuit PZD is driven by a timing pulse TP generated by a carriage position sensor FDP during reciprocative movement of the carriage. 
     When the printing data is stored in the printing memories PCM1 and PCM2 in this manner, the control section CC clears the printing dot counter PC and the line counter LC to initialize the addresses of the printing memories PCM1 and PCM2 by setting the signal line l C  to logic level &#34;0&#34;. After setting the black and red read/write signal lines l RW1  and l RW2  to logic level &#34;1&#34; (read state) and confirming that a busy signal line l Bsy  from the printer control section PCC is at logic level &#34;1&#34; (not in the busy state), the control section CC sets a signal line l PF  to logic level &#34;1&#34; and a signal line l PB  to logic level &#34;0&#34; to instruct the printer control section PCC to start printing. Then, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34; (busy state), sets a drive signal line l F  of the linear motor LM to logic level &#34;1&#34;, and sets a drive signal line l B  to logic level &#34;0&#34; so as to drive the carriage toward the left from its home position (right-hand position on a printing paper sheet P). During this time period, the timing pulses TP from the carriage position sensor FDP are detected. In response to the timing pulse immediately next to that corresponding to the printing start position, the printer control section PCC sets the signal line l Bsy  to logic level &#34;1&#34; so as to signal to the control section CC that the printing data may be transmitted. In response to this, the control section CC sets a signal line l REQ  to logic level &#34;0&#34; to signal to the printer control section PCC that the data on data lines D P1  and D P2  is valid. Then, the printer control section PCC sets the signal line l Bsy  to logic level &#34;0&#34; (busy state) to allow write of printing data into the printing memories PCM1 and PCM2. In response to the next timing pulse TP, the driver circuit PZD is driven through the signal lines l B1  and l R1  to print in black and red in accordance with the state of the most significant bit of first byte of the 126×7 dot matrix. Since the printing data is &#34;00&#34; for black and red as shown in FIG. 11A, a space is printed. When this printing is completed, the printer control section PCC sets the signal line l Bsy  to logic level &#34;1&#34; to signal to the control section CC that the next printing data may be transmitted. Then, the control section CC increments the printing dot counter PC by one through the signal line l PC  to increment the addresses of the printing memories by one. The next printing data is supplied to the data signal lines D P1  and D P2 . The control section CC sets the signal line l REQ  to logic level &#34;0&#34; to indicate that the data on the data signal lines D P1  and D P2  is valid. The printer control section PCC reads the data from the printing memories PCM1 and PCM2 and performs printing in response to the next timing pulse. 
     In this manner, the data of the most significant bit of each 1×7 dot pattern, that is, the first row of the 126×7 dot matrix, is printed to the left. During this time period, a coincidence circuit CO monitors coincidence between the contents of the printing dot counter PC which is incremented by one upon every printing operation and of the printing dot register PR. When coincidence occurs, the control section CC detects completion of printing of first 126 dots, clears the contents of the printing dot register PR through the signal line l PR , and sets the signal lines l PF  and l PB  to logic levels &#34;0&#34; and &#34;1&#34;, respectively. Subsequently, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34;, and the drive signal lines l F  and l B  to logic levels &#34;0&#34; and &#34;1&#34;, respectively so as to drive the carriage to the right and to start printing to the right. The pulse motor PM is driven to feed the printing paper sheet by one dot pitch. As in the case of printing to the left, in response to the timing pulse immediately next to that corresponding to the printing start position, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;1&#34; to signal to the control section CC that the printing data may be transmitted. The control section CC then sets the signal line l REQ  to logic level &#34;0&#34; to indicate that the initial data for printing the second row to the right, that is, the 126th dot, is valid. Then, the printer control section PCC receives the printing data and executes printing in response to the next timing pulse TP. Thereafter, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;1&#34; to indicate that the next printing data may be transmitted. Since the next printing must be performed to the right-hand side, the control section CC decrements by one the count of the printing dot counter PC to thereby decrement the printing memory address by one. The control section CC transfers the data of the 125th dot to the data lines D P1  and D P2 , sets the signal line l REQ  to logic level &#34;0&#34;, and performs printing in response to the next timing pulse TP. In this manner, the second row of the 126×7 dot matrix of black and red printing data is printed to the right. As in the case of printing the first row, when the coincidence of the printed dot number with 126 dots is detected by the coincidence circuit CO, the control circuit CC increments by one the count of the line counter LC through a signal line l 1 . An output signal line l 2  of the line counter LC is for detecting if four reciprocative printing operations of the carriage have been completed, that is, if one line has been printed. Since only one reciprocative movement has been completed in this case, no output is produced from the output signal line l 2  in this case. The control section CC sets the printing dot register PR to 125, and sets the signal lines l.sub. PF and l PB  to logic levels &#34;1&#34; and &#34;0&#34; to instruct printing of the third row of the 126×7 dot matrix. In response to this, the printer control section PCC sets the busy signal line l Bsy  to logic level &#34;0&#34; to perform paper feed of one dot pitch and sets the drive signal lines l B  and l F  of the linear motor LM to logic levels &#34;1&#34; and &#34;0&#34; to perform the printing to the left. The printing direction is reversed when the coincidence circuit CO detects another coincidence of the printed dot number with 126 dots. In this manner, four reciprocative movements of the carriage, that is, printing of one line, are completed. When printing of one line is completed, the control section CC receives an output from the output signal line l 2  of the line counter LC to thereby detect that the 126×7 dot matrix, or one line, is completed. 
     Since the scale numerals have been printed, the control section CC, referring to the busy signal line l Bsy , instructs to the printer control section PCC through a signal line l FD  to perform paper feed of one dot pitch. In response to this, the printer control section PCC performs paper feed of one dot pitch. Subsequently, the control section CC stores the data of the scale lines to the printing memories PCM1 and PCM2, as shown in FIG. 11B. Since printing of the scale lines involves only printing in black, data of logic level &#34;0&#34; is stored in the printing memory PCM2 corresponding to printing in red. In the same manner as printing of the scale numerals, printing of the contents in the printing memory PCM1 corresponding to printing in black is executed by four reciprocative movements of the carriage, thus completing scale line printing instructed by input through the keys  0  and   ; the keys  5 ,  0 ,  + , and   ; and the keys  5 ,  0 ,  - , and   . 
     When the keys  3 ,  0 ,  +  and    are depressed to enter the graph printing data, the control section CC judges that the graph printing mode is initiated. Since the printing is detected to be in the positive direction by the entry of the key  + , the control section CC calculates the print start position with reference to the printing position of the scale numeral +50. The printing position of the scale numeral +50 is the 50th dot to the right from the central scale line, and the printing position of a bar for +30 is the 30th dot to the right from the central scale line, as shown in FIG. 9. On a 126 dot row, 30 dots are printed in black from the 32nd dot from the right side of the printing paper sheet P. Since the printing is to be performed in the positive direction, the printing data is stored in the printing memory PCM1 together with the item (01 in FIG. 9). Since printing in red is not performed in the graph printing (in the negative direction), data of spaces for 126 dots is stored in the printing memory PCM2, as shown in FIG. 11C. 
     After the graph printing data is stored in the printing memories PCM1 and PCM2 in this manner, the control section CC executes printing by four reciprocative movements of the printer carriage as in the case of printing of the scale numerals. Thus, the graph is printed solid as in the case of item 01 in FIG. 9. When printing is completed, the control section CC stores the data on the central scale line together with data of spaces in the printing memory PCM1 and also stores the data corresponding to spaces in the printing memory PCM2, as shown in FIG. 11D. Printing of the central scale line is completed by the four reciprocative movements as described above. When the keys  2 ,  5 ,  -  and    are depressed to enter the graph printing data, the control section CC recognizes the graph printing mode and printing in the negative direction by the entry of the key  - . The control section CC calculates the printing position with reference to the scale numeral -50. The printing position of the scale numeral -50 is the 50th dot to the left from the central scale line, and the printing position is calculated to be the 25th dot to the left from the central scale line. On a 126 dot row, the spaces continue for 61 dots from the right side of the printing paper sheet P, the central scale line is printed at the 62nd dot, and the bar for -25 is printed from the 63rd dot to the 87th dot, the spaces continue from the 88th dot to the 113th dot, and finally, the item 02 is printed. 
     The printing data as described above is stored in the printing memories PCM1 and PCM2 separately. Since printing is to be performed in the negative direction, the graph printing data from the 63rd dot to the 87th dot is stored in the printing memory PCM2, wherein the 63rd dot to the 86th dot correspond to the graph staggered pattern, and the 87th dot corresponds to the vertical line. The central scale line at the 62nd line and the item data are stored in the printing memory PCM1, as shown in FIG. 11E. The control section CC performs printing by the four reciprocative movements of the printer carriage to print the red staggered pattern of 25 dots in the negative direction. Thereafter, the central scale line is printed in a similar manner to complete printing of the graph printing data. 
     When the keys  2 ,  + , and    are entered, printing of item 03 is similarly performed as shown in FIG. 9. When the keys  4 ,  0 , and    are entered, the graph printing of item 04 as shown in FIG. 9 is performed. 
     The numbers of items 01 to 04 are produced from the counter incorporated inside the control section CC. 
     According to the embodiment as described above, a reference value or a target value is set at the center. If the input data exceeds the reference value, data is printed in black to the right of the reference value. If, on the other hand, the input data is below the reference value, it is printed in red to the left of the reference value. In this manner, the polarity of each item may be indicated easily so that the current status with reference to the target value may be readily evaluated to improve the working efficiency and the like.