| 摘要 |
PURPOSE:To reduce an area occupied by a data bus on a chip at forming a microcomputer of an integrated circuit by setting up the number of constitutional bits of the data bus less than that of an address data and using 2 machine cycles or more to execute a call instruction or an interruption. CONSTITUTION:The number of constitutional bits of the bus line for transferring return address data formed by an incrementer 12 at the execution of a call instruction in a subroutine to a stack area 16 formed in a general memory is set up less than the number of bits of a program register and >=2 machine cycles are used to execute the call instruction. Gate circuits 21-23 send the output of the high-order bit (or low-order bit) of the incrementer 12 to the data bus in the 1st machine cycle and gate circuits 19, 20 send the output of the low-order bit (or high-order bit) of an address latch 13 for storing a return address outputted from the incrementer 12 to the data bus 14 in the 2nd machine cycle. The return address data are divided and stored in the stack area 16.
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