From: John Coffman <johninsd@gmail.com>
Date: May 12, 2011 11:14:52 AM PDT
To: n8vem@googlegroups.com
Subject: Re: [N8VEM: 9966] Re: Z84C0010PEC for $3.92 10MHz Z-80 Good price?
Reply-To: n8vem@googlegroups.com

Douglas,

The floppy driver has delays of 12-16us done as loops @ 4Mhz.  For that matter, even the interrupt driven driver has similar delays.

CPU speed can be measured against the UART clock -- character send timing.

--John

On 05/11/2011 09:00 PM, Douglas Goodall wrote:
I don't know of any timing loops in the bdos
and I am going to address the ones in the
hardware drivers.

There is hope, but the bios has to be able to know 
what speed the system is running at. Either we have to tell
it, or it has to sense it, perhaps from skew with the ds chip.

Douglas

On May 11, 2011, at 8:33 PM, John Coffman wrote:
To All,

The speed limitation of the SBC v1 & v2 comes from the odd timings of the Z80:

        Data reads take about 2 clocks
        Instruction fetches take about 1.5 clocks
        Data writes take about 1 clock !!!!!

Since the Z80 SBC's run at 0 wait states, the SRAM limitation will be the Write timing (1 clock).  The ROM limitation will be the Instruction Fetch timing (1.5 clocks).  With 55ns SRAM and 90ns EPROM, 12Mhz seems to be the limit for me.  16Mhz was never very reliable; I think it may have hit the EPROM limit.  I have not checked 14.3182Mhz.

However, remember the timing loops spread through much of the CP/M code:  the time counter constants are calculated for 4Mhz.  For this reason, I only run at 4Mhz.  It was fun to try the timing tests.

--John

On 05/11/2011 05:13 PM, Douglas Goodall wrote:
One of the builders said he had his SBCV2 running well at 10MHz with 74HCT parts and this CPU.

I just wanted to go along with his formula, hoping for the best.

Douglas

On May 11, 2011, at 3:20 PM, Sergey wrote:

Jameco has 8 MHz Z84C0008PEC for $1.95 (Part number 280516). I am not
sure if you wanted the 10 MHz part specifically, but I think somebody
mentioned that 8MHz CMOS part will work on the higher frequency too...

On May 11, 1:55 pm, Douglas Goodall <douglas_good...@mac.com> wrote:
I just ordered three of these. It took them three weeks to ship, but I haven't been able to beat the price for the 10MHz part.

 abra10mhz.png
232KViewDownload
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