| 摘要 |
PURPOSE:To remarkably improve an arithmetic processing speed and to simplify a circuit and a processing program by using a specific function unit to enable an I/O unit to be directly accessed. CONSTITUTION:The specific function unit 24 is connected to the I/O bus of I/O units 23(23-1-23-5) in common, and thereby an optional I/O unit 23 can be directly accessed by the unit 24. The unit 24 includes an arithmetic processing function such as a microcomputer in its inside and is allowed to execute operation based on external information and access an external apparatus directly through the unit 23. During the direct access of the unit 23 from the unit 24, a CPU unit 22 can be temporarily held. Thereby, the unit 24 is connected to the unit 22 through holding circuits 2, (acknowledge) 3. When the unit 24 uses the unit 23 in common with the unit 22, the unit 24 can be allowed to have priority by a CPU holding signal.
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