Re: Apple II Bus Timing

[jaqas@my-deja.com]

Thanks for the feedback Patrick.  I had already seen Chris Wards
schematic and my design is very similar using polled IO rather than DMA
to transfer the data.  Perhaps not as fast as possible but better than
floppies.  My issue was that reading the same sector (or drive
configuration information) would return incorrect data in some bytes
approx 25% of the time.

My conclusion after exhausting everything else was that this was
perhaps a timing issue and the comment in the book regarding data hold
time for the 6502 and difference between between the 6502 and bus
clocks gave me some hope that is the case.  I will try your suggestion
re generating the 6502 phi2 signal and see what effect it has.

Regards.... Andrew


In article <39F41BE5.B2439834@topmail.de>,
  Patrick Schaefer <patrick.schaefer@topmail.de> wrote:
> Andrew Quinn schrieb:
>
> > The apple bus provides o0 (rather than o2) for bus timing and this
appears
> > to lead o2 due in the timing diagrams but I cannot find timing
details of
> > this lead so I can hold the data on the bus a little longer.
>
> phi0 is the clock signal that drives the 6502, Apple's phi1 is its
> complement. From this phi0 the 6502 derives phi1 (the real one, not
> Apple's) and phi2, to which its timing is related. Apple phi0 leads
6502
> phi2 by a few ns.
>
> The /Device_select and /IO_select signal become active with Apple
phi0,
> this can be used to drive 74LS373 D-latches as outputs and 72LS245
> buffes as inputs.
>
> To generate a 6502 phi2 signal to drive 6522 VIAS, 6581 SIDs or things
> like that, invert phi0 and NOR it with Q3. This can be done using 1/2
> 74LS02, one as an inverter and one as a NOR. The resulting singal is
not
> symmetric, but it works.
>
> For a quick and dirty implementation of an IDE interface, look at
> http://home.freeuk.net/c.ward/6502/schematics/ide.gif
> However, to make it fast, you will need DMA. And to make it really
fast,
> you will need some kind of burst DMA with 2..3 transfers in one cycle
> (like the Z80 Softcard does).
>
> Patrick
>


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