On Fri, Apr 22, 2016 at 3:15 AM, Alexis Kotlowy <thrashb...@kaput.homeunix.org> wrote: > http://kaput.homeunix.org/~thrashbarg/z80.pdf > > Looking at this Z80 datasheet (page 20 of the PDF) the timing diagrams > say the /WAIT signal is sampled on the falling edge of clock state T2. > If it is active, additional cycles are introdced between T2 and T3. This > only occurs on op-code fetch, memory reference, input-output and > interrupt acknowledge cycles.
Thanks, but I'm not convinced by that particular part of the datasheet. I see where it says: 1) "The Z80 CPU executes instruction by proceeding through a specific sequence of operations: *Memory read or write *I/O device read or write *Interrupt acknowledge" 2) "Machine cycles can be extended [...] by the insertion of one or more Wait states by the user." The first of those statements omits that there can be M cycles which are of none of those stated cycle types, and are used purely for internal operation. For example, an ADD HL, BC instruction has three M cycles, but only the first is a fetch, and the other are internal operations. The second and third M cycles have seven T-states between them; probably one of those M cycles has three T-states and the other has four[*]. I don't see where it says that ONLY the op-code fetch, memory reference, input-output, and interrupt cycles can be extended, and I don't see anything in the datasheet or user manual that definitively states that the second and third M cycle of that 16-bit ADD instruction can't be extended with wait states by /WAIT being asserted at the faling edge of T2 of those M cycles. On the other hand, if someone with personal experience has verified that internal-only M cycles can't be extended by asserting /WAIT, that's would answer my question. I'm starting to think that I'll actually have to kludge up a test circuit to find out. Best regards, Eric [*] I thought at one point I saw Zilog or Mostek Z80 documentation that gave the specific details of every M cycle of every instruction, but I can find such a thing at the moment. :-(
