| 摘要 |
PURPOSE:To decrease the capacity of a RAM by providing a decoder for decoding an address stored in an address storing means and outputting a bit of modification information for modifying write information and an arithmetic instruction. CONSTITUTION:The RAM 1 is a RAM to which a microcomputer can execute read-out and write. A register 2 holds a bit of information to be written to the RAM 1 inputted through an input line 10. An address register 3 holds an address to execute read-out and write of the RAM 1 inputted through a signal line 11. A decoder 4 is controlled as to whether it is effective or ineffective by the operation mode of an information processor, decodes the address of the RAM 1 which the address register 3 holds, and outputs a data corresponding to this address and an arithmetic instruction. An arithmetic circuit 5 inputs the information of the register 2 and the data from the decoder 4, executes an arithmetic operation based on the arithmetic instruction outputted from the decoder 4, and writes its result to the RAM 1.
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