1. Field of the Invention
The present invention relates to a program mode acess control system by which a plurality of input output devices are controlled by one input output control device and a rapid program mode access is made between this input output device and a central processing device.
2. Description of the Related Art
The construction of an input output control device which controls an input output device such as a magnetic tape device, a magnetic disc device, a magnetic floppy device, a line printer, etc., usually comprises a microprocessor, and corresponds to the construction of the input output device. Therefore, a standardization of the input output device is desired.
The conventional processing device, for example, has the construction, described as follows. A processor bus couples a central processing unit, a main memory device and a channel device, a plurality of input output control devices are connected via the channel device and a common bus, and each input output control device is connected to an input output device such as a magnetic tape device, a magnetic disc device, a magnetic floppy device, a line printer, or a display device etc.
Each input output control device is formed by an internal control portion formed by a microprocessor, etc., a receiver driver, a control register, an input output interface circuit, etc. One or a plurality of the same kind of input output devices are connected to the input output interface circuit.
As described above, the conventional input output control device provides a control register formed by a plurality of registers, sets the control information in the control register and reads out the content thereof to carry out the desired control operation. Thus, the control system due to the wired logic is conventionally used. However, due to recent developments in microprocessors, the control system can now be operated with firmware, and a flexible control for the input output device is now possible, which leads to a reduction of the hardware needed.
The construction of the control system on the firmware by such a wired logic corresponds to that of the input output device, such as the magnetic tape device, magnetic disc device, display device, etc. Thus when a plurality of the input output devices are controlled, the control system is restricted to that of one kind of input output device.
However, control of a plurality of the input output device should be made by the same input output control device. In such case, the operating speed of the microprocessor (the internal control portion) in the input output control device cannot follow the access operation for the high speed control register due to command checks from the central processing device side. Further, when using hard logic, much hardware is required for the control register. Thus a unified control of a plurality of different kinds of input output devices becomes difficult.