| my latest Z80 SBC [message #9182] |
Wed, 06 October 2021 15:25  |
norwestrzh
Messages: 196
Registered: November 2015
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Senior Member |
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This is my newest Z80 SBC. It is based on Grant Searles 9-chip Z80, but with some enhancement. There is a bank toggle to access the other half of the 128k SRAM, and an improved reset circuit. I found the original reset design to be unreliable. This SBC is currently running at 16 MHz. I've got a faster SRAM on order to see if it is possible to run at 20 MHz. It runs Plasmo's ASCII art program (compiled with the Hitech C compiler) in about 19 seconds. It uses both the CMOS versions of the Z80 and SIO. A number of baud rates are available for the two serial ports: 38.4k or 115.2k can be set by a jumper and change of the UART oscillator. Others can be set up with changes to the UART initialization code. Serial connections are via the common, and inexpensive, 2102 style TTL to USB adapter. The logic is SMT 74LS. That little, white bodge wire is not there because of a mistake on the PCB. I damaged a trace trying to solder the LS138 (I'm still trying to learn how to work with SMT). A 27C256 UVEPROM can be used for the firmware, or I now use a Winbond W27C512 (either half of the 64k chip can be accessed with an on-board jumper). The original plan was to power it with a wall wart, but I discovered that it can be powered directly from the USB port. I now regret not having a jumper to select either external power to the IDE-CF adapter, or internal power via pin 20 of the interface. *frown* That's what the yellow/red jumper wire is for.
Currently running CP/M 2.2 with sixteen 8 MB "drives", and a number of compilers/interpreters: BASIC, FORTRAN, C, Pascal, FORTH, PL/I, and of course, assembler. I intend to use it for programming applications.
Roger
[added 10/7: Got a few 50 n.s. SRAMs (Alliance AS6C1008) in the mail today. Very pleased that this SBC now runs at 20MHz with a 115.2k baud console. It runs ZEXALL in about 34 minutes!]
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[Updated on: Thu, 07 October 2021 19:29] Report message to a moderator |
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| Re: my latest Z80 SBC [message #9189 is a reply to message #9187] |
Sat, 09 October 2021 16:53  |
plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
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Senior Member |
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Running Grant Searles's Z80 to 20MHz is an interesting result because I didn't think to overclock SIO which is a 10MHz part. I had been successful in overclocking Z80 to 33MHz for selected Z80 and reliably to 29.5MHz (29.4912MHz to be exact). However, the I/O of such overclocked system is based on either CPLD emulation of serial port or KIO (Z84C90). Never did thought about running SIO to 29.5MHz...hmmm...
Edit, Moved the remaining discussion to Simple80 topic so not to hijack this thread
Bill
[Updated on: Sat, 09 October 2021 17:44] Report message to a moderator |
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