a video game apparatus incorporating the present invention may be as shown in fig1 . as shown , a main frame 1 of the video game apparatus which plays a game is connected to a television set 2 and to a pair of joysticks 3 and 3 distinguished as a and b . connectors ( not shown ) are used for the connection of those components . the main frame 1 is provided with a power switch 1a and a receptable 1b for receiving a rom pack storing a game program ( not shown ). each of the joysticks 3 and 3 is provided with a select key 3a for selecting either a one - player mode or a two - player mode , a start key 3b for starting the game , and a stick 3c for moving an object on the screen in many directions , for example , right , left , up , down , and oblique . the joysticks 3 and 3 have the same configuration and may be connected to either connector of the main frame 1 . fig2 shows a configuration of a circuit contained in the main frame 1 , including reference numeral 1 designates processing unit ). a ram 13 , a rom 14 , a buffer 15 for common output , a buffer 16 for key in , and a video composing circuit 17 are interconnected through a bus 12 . the output signals from the cpu 11 are applied to set input terminal s reset input terminal r of a flip - flop ( ffa ) 19 respectively . the output signals from the reset output terminals q are connected to the cpu 11 . the ram 13 includes a text area for saving a table , a work area made up of an operation register , an area for saving character codes , and another area made up of an fl register for storing the mode , the one - player mode or the two - player mode , selected by the select key 3a of the joystick 3 . &# 34 ; fl = 0 &# 34 ; indicates selection of the one - player mode , and &# 34 ; fl = 1 ,&# 34 ; the two - player mode . the rom 14 is a rom pack storing a game program and a character generator , and is set into the receptacle 1b . the buffer 15 temporarily stores sampling data applied as a sampling signal to key circuits 3d and 3d as fixed contacts ( not shown ) of the keys 3a , 3b and of the stick 3c provided in the joystick 3 , in order to detect the operation of the keys and the stick . the sampling data is sequentially fed from the cpu 11 . the output signal from the key circuits 3d and 3d is respectively applied through the masking buffers 20a and 20a to a buffer 16 for keying in . the output signal is temporarily stored in the buffer 16 and then is applied to the cpu 11 through the bus 12 . the input terminals of the buffers 20a and 20b are respectively coupled with the reset terminals q . only when &# 34 ; 1 &# 34 ; appears at the terminal q , that is , only when the flip - flop 19 or 18 is in a reset state , does it read the output of the corresponding key circuit 3d . the results of the game through a combination of the cpu 11 , the ram 13 and the rom 14 are applied through the bus 12 to the video composing circuit 17 . in the video composing circuit 17 , the results are transformed as a video signal which is visually displayed by the television set 2 . the operation of the video game apparatus thus arranged will be given referring to fig3 a & amp ; 3b . the main flow of the operation is power on ; mode selection , i . e . one - player mode or two - player mode ; operation of start key 3b ; execution of game ; and game over . a one - player mode as selected by the select key 3a will first be given . when the power is on , the cpu 11 executes step s1 where the flip - flops 18 and 19 are reset , and where the initial values are set in various types of resistors and flags . then , step s2 is executed . in this step s2 , sampling data transferred from the cpu 11 is sequentially updated , and it is judged whether or not the keys and the stick , 3a , 3b and 3c are operated . if no key operation is detected , the program flows to step s3 . in this step , it is judged whether or not a game is actually being played following the start of the game . if the game is not being played , the program returns to step s2 , and repeats steps s2 and s3 until the key is operated . at this time , if the select key 3a is operated for a one - player mode , in step s2 this state is judged as &# 34 ; key on &# 34 ; and step s4 is executed . in step s4 , it is judged whether or not the start key 3b of the joystick a has been operated . since the key operated at this time is the select key 3a , &# 34 ; no &# 34 ; is produced and the program advances to step s5 . step 5 likewise judges whether or not the start key 3b of the joystick b is operated or not . therefore , &# 34 ; no &# 34 ; is produced and the cpu 11 executes step s6 . in this step s6 , it is judged which mode , the one - player mode or the two - player mode , has been seleted by the select key 3a and whether or not the other key has been operated . at present , since the one - player mode has been selected , the cpu 11 executes step s7 and loads &# 34 ; 0 &# 34 ; into the fl register of the ram 13 . then , it executes step s2 again and continues the key sampling until the next key operation is performed . let us assume that the joystick b is used for playing the game , and that the start key 3b thereof is operated . the program flows through step s4 to step s5 . in step s5 , &# 34 ; yes &# 34 ; is given . therefore , the cpu 11 sends a set signal to the set input terminal s of the flip - flop ( ffa ) 19 ; the ffa 19 is set as shown in step s8 , and then flows to step s9 . at this point , a game start mode for the one - player mode is completed . after the start of the game , the player operates the stick 3c of the joystick b or a shooting button ( not shown ) to play the game . upon operation of the stick or button , the program jumps from step s6 to step s10 . in step s10 , it is judged in what direction the stick 3c is turned or whether or not the shooting button is pushed . next , in step s11 , game processing such as change of the picture on the screen and the addition of scored points is executed on the basis of the judment results . after completion of step s11 , step s12 is executed to determine whether fl is &# 34 ; 0 &# 34 ; or not , viz ., the selected mode is the one - player mode or the two - player mode . since the present mode is the one - player mode , &# 34 ; fl = 0 &# 34 ; and step s13 is executed . in this step s13 , it is judged whether or not the game under execution is over . if the result of the judgement is &# 34 ; no ,&# 34 ; step s2 is again executed and the game is continued . if it is &# 34 ; yes ,&# 34 ; step s14 is executed . in this step s14 , the flip - flop ( ffb ) 18 and the flip - flop ( ffa ) 19 are reset or initialized . next , step s15 is executed . this step s15 displays the end of the game or the total of scored points on the screen of the television set 2 . after completion of this step , the program returns to step s2 and the video game apparatus is ready for the next game . as described above , if the start key 3b of the joystick b is pushed , the flip - flop ( ffa ) 19 is set and disables the buffer 20a in reading the sampling data from the key circuit 3d . under this condition , nothing is input if the joystick a is operated in any way . on the other hand , if the start key 3b of the joystick a is pushed at the start of the game , the program execution jumps from step s4 to s16 . in this step , the flip - flop ( ffb ) 18 is set and the reading operation by the buffer 20b is made inoperative to inhibit inputting by the joystick b . a two - player mode as set by the select key 3a will be described . power is first turned on . when a game to be played is a new one , the cpu 11 executes the key sampling processing of step s2 through step s1 . when the game is the same as before , the cpu 11 executes the processing that follows step s15 . when the select key 3a is operated to set up the two - player mode , the cpu 11 executes steps s4 , s5 and s6 in that order . in step s6 , the two - player mode is confirmed , and the program execution step of step s6 jumps to step s17 . in this step , &# 34 ; 1 &# 34 ; is loaded into the fl register of the ram 13 . if it is desired to first operate joystick b to play the game , the start key 3b of the joystick b is operated . then , the program is sequentially executed in the route of steps s4 , s5 , s8 and s9 , and the game starts . subsequently , in response to operating the stick 3c of the joystick b or the shooting button , steps s10 and s11 are sequentially executed , as in the previous case . in step s12 , &# 34 ; no &# 34 ; is given then fl = 1 at present and since step s18 is executed . in this step s18 , it is judged whether or not the video game apparatus has failed due to the fact that the operation of the stick 3c of the joystick b fails to follow the motion of the object on the screen . if the result of the judgment is &# 34 ; no ,&# 34 ; the cpu 11 returns to step s2 , thereby allowing the game to continue to be played by operating the stick 3c of the joystick b . on the other hand , if the result is &# 34 ; yes ,&# 34 ; the cpu 11 goes to step s19 to change the state of the flip - flop ( ffb ) 18 from the reset state to the set state , and to change the state of the flip - flop ( ffa ) 19 from the set state to the reset state . then , the other player gains the right to operate the joystick . then , step s20 is executed to change the screen for the other player . since in step s19 , the flip - flop ( ffb ) 18 is set , the buffer 20b is made inoperative in the reading operation . on the other hand , because the flip - flop ( ffa ) 19 is reset , the buffer 20a is placed in a read permission state . accordingly , the game may be continued using the joystick a . subsequently , the game is continuously played alternately by both players , going back and forth between joystick b and joystick a until the game is over . when both the players finish their games , the program jumps back from step s21 to step 14 . then , the flip - flops 18 and 19 are reset and the video game apparatus stands ready for the next game . if the start key 3b of the joystick a is pushed at the start of the game , the order of playing the game by the players is reversed going back and forth between joystick a and joystick b . the operation by the cpu 11 is performed as in the previous manner . in the two - player mode , the game is started by the player who first pushes the start key . at this time , the operation of the joystick of the other player is void . while in the above - mentioned embodiment , the select key 3a is mounted to the joystick 3 , it may also be mounted to the main frame 1 of the video game apparatus . provision of the two flip - flops for masking the outputs of the joysticks 3 and 3 , may be replaced by raising masking flags in the ram . as described above , the output signals of the key circuits 3d are controlled by the masking buffers 20a and 20b , respectively . alternatively , the input signals to the key circits 3d and 3d may be masked by controlling the output signals from the buffer 15 . it should be understood that the present invention may be variously changed and modified within the scope of the present invention .
in a video game apparatus , a first joystick and a second joystick each contain a stick , a game start key and a mode select key . a control circuit controls the video game apparatus in the following manner . in a one - player mode as selected , only the output signal from the joystick whose start key is operated , is supplied to the main frame of the video game apparatus . in a two - player mode as selected , the output signal from the joystick whose start key is operated is supplied to the main frame . in turn , a game is started . with the progression of the game , the output signals from the first and second joysticks are alternately applied to the main frame .