| Resurrecting EaZy80, a forgotten glue-less 22MHz Z80 SBC. [message #10511] |
Sun, 19 November 2023 18:14  |
plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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Senior Member |
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EaZy80 was a 4-1/2 year pc board design that was forgotten. It was not assembled and powered up until recently when I rediscovered it while rummaging through pc boards. The design approach was a glue-less Z80 SBC very similar to Simple80 but used KIO (Z84C90) for I/O. KIO is much faster than Simple80's SIO thus can run at much higher CPU clock. The nominal operating frequency of EaZy80 is 22MHz, but it has been overclocked to 31MHz successfully. Second picture shows it working with Simple80's CF board to run CP/M.
I generally design with CPLD, but this is one of few designs without CPLD, so it is easy to find parts and put one together. While the parallel CF interface is faster, KIO has plenty of IO lines to bit-bang SD disk and talk to DS1302 RTC, so a CP/M computer can be created without any glue logic.
EaZy80 has 128K of RAM. The 2nd bank of 64K is accessible by manipulating KIO's PC0 output. Bank sharing routines are installed at high end of both RAM banks, so data can be shared between two banks. Ladislau Szilagyi has enhanced HiTec C and TE editor for Simple80 based on these bank sharing routines. I believe the same routines will also work for EaZy80.
Another thing to explore is replacing the 128K RAM with 512K RAM and port RomWBW to it. However, I don't know how to do that with 8 banks of 64K RAM, but with the addition of a quad OR gate (7432), 16 32K banks are possible which definitely will support RomWBW.
I created a homepage for EaZy80 here:
https://www.retrobrewcomputers.org/doku.php?id=builderpages: plasmo:eazy80:rev0pcb:eazy80r0home
Bill
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