22 May
2013
22 May
'13
4:28 a.m.
On Tue, May 21, 2013 at 4:39 PM, Chuck Guzis <cclist at sydex.com> wrote:
A few years back, Herb Johnson opened a discussion of
this on his web
site. The conclusion was that a 4 MHz Z80 was indeed fast enough to do
this with programmed I/O and DD 8" disks (500KHz data rate) and that it was
*barely* possible to do at 2 MHz Z80 set up correctly and not at all with a
2 MHz 8080.
There are hardware issues also relating to your selection of FDC. The
general consensus and experience of the N8VEM CP/M board builders is that
programmed IO with a 8 MHz and up Z80 and a modern 1.44 MHz floppy and a
9266 FDC works perfectly. I assembled a system this winter and that worked
perfectly. Obtaining 8+ MHz chips for modern Z80 designs is non trivial
and involves lots of ebay and searching.
Someday I will remove my CPU canned osc, locate a TTL output function
generator, and figure out exactly what the minimum is. The disk io v3
board has headers and software support for a 8 inch floppy and if I can
locate one I could do pretty extensive testing of different disk
technologies. This type of test with a live system, lots of different
drive types, and a ttl output function generator in place of CPU clock
would certainly prove once and for all what is required for what drive
technology.