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> | ||
Revision as of 15:31, 1 June 2015
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 stops CPU clock signal. 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...