| 摘要 |
PURPOSE:To simplify constitution and to prevent a load from being applied on a CPU by storing command data in each memory area at the time of writing each command data and reading each command data by designating each memory area at the time of reading back. CONSTITUTION:In case of performing write on a control register 22-1, a RAM 27 receives a write signal and the command data passing a data bus 21, and stores the command data in the memory area corresponding to the control register 22-1. Next, in case of reading back the command data in the control register 22-1, stored command data is read out from the memory area of the control register 22-1 by the input of a read signal by the RAM 27, and the command data is sent to the CPU 20 via the data bus 21. In such a way, it is possible to make a three-state buffer unnecessary, and the number of out of the data bus 21 can be also reduced. Also, since read back can be performed only by designating an address to the RAM 27 by the CPU 20, the load on the CPU 20 can be reduced. |
