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Talk:Contended I/O: Difference between revisions
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(ULA really makes Z80 to go WAIT state instead of HALT it) |
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IMHO the "... the ULA '''halts''' the processor" is not the best phrase, because there is a HALT instruction in Z80 assembly, which really '''halt''' the CPU and the processor is '''halted''' while an interrupt arrived. Hmm... o.k. not exactly, because Z80 do NOPs to refresh memory. | IMHO the "... the ULA '''halts''' the processor" is not the best phrase, because there is a HALT instruction in Z80 assembly, which really '''halt''' the CPU and the processor is '''halted''' while an interrupt arrived. Hmm... o.k. not exactly, because Z80 do NOPs to refresh memory. | ||
This situation the ULA really pulls the "/WAIT" pin of CPU, and Z80 adds "empty" clock cycles while /WAIT is low. BTW: while Z80 waits, does not refresh the memory, so a long wait cycle can "erase" the DRAM... | This situation the ULA really stops CPU clock signal. <del>pulls the "/WAIT" pin of CPU, and Z80 adds "empty" clock cycles while /WAIT is low. BTW: while Z80 waits, does not refresh the memory, so a long wait cycle can "erase" the DRAM...</del> | ||