| 摘要 |
<p>PURPOSE:To reduce the number of registers without degrading CPU functions in a microprocessor. CONSTITUTION:The I/O shared port for CPU transfers information supplied to port part 3 to the data bus 4 direction through input circuit 1 by an INPUT instruction, and latch-holds information sent from CPU through data bus 4 in output circuit 2 consisting of registers by an OUTPUT instruction, and then transfers it to the terminal equipment direction from read port part 3 by the next OUTPUT instruction. The microprocessor has m-bit I/O ports P1 to Pn consisting of m-number I/O shared ports like this. Unused ports are not connected to the external, and can hold temporarily contents of CPU in input circuit 2 by OUTPUT and INPUT instructions, so that it is possible to share the register of input circuit 2 with registers of CPU.</p> |
