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Re: A simple CP/M Z80 SBC without glue logic [message #6144 is a reply to message #6142]

Fri, 15 March 2019 08:47

wsm
Messages: 232
Registered: February 2017
Location: AB, Canada

Senior Member

Plasmo: Tying MREQ* to CS* of the RAM and ROM would work but the switching of OE* might require some glue. At power-on the ROM's OE* needs to be low and the RAM's high which can be done via pull-down / pull-up. After the copy, the ROM's OE* can go high from a KIO port. HOWEVER, the RAM's OE* needs to be tied to RD* or possibly NOT WR* after the switch to avoid bus contention during RAM writes i.e. simultaneous RD* and WR* from/to RAM.

etchedpixels: The KIO's CS* could be tied to a high address bit and that should work including if interrupts are enabled i.e. IORQ* active but RD* and WR* inactive. If the KIO is the only I/O device then it might be simpler to just tie CS* low and let the KIO decode IORQ*, M1*, RD* and WR*.

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[Message index]

		A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 14 March 2019 08:20
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Thu, 14 March 2019 10:50
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 14 March 2019 11:09
		Re: A simple CP/M Z80 SBC without glue logic By: mikemac on Thu, 14 March 2019 16:39
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Thu, 14 March 2019 18:01
		Re: A simple CP/M Z80 SBC without glue logic By: etchedpixels on Fri, 15 March 2019 05:21
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Fri, 15 March 2019 08:47
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Fri, 15 March 2019 09:11
		Re: A simple CP/M Z80 SBC without glue logic By: etchedpixels on Fri, 15 March 2019 09:39
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Fri, 15 March 2019 10:15
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Sat, 16 March 2019 06:41
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 04 April 2019 05:34
		Re: A simple CP/M Z80 SBC without glue logic By: b1ackmai1er on Thu, 04 April 2019 06:29
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 04 April 2019 07:28
		Re: A simple CP/M Z80 SBC without glue logic By: etchedpixels on Thu, 04 April 2019 09:56
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 04 April 2019 13:58
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Thu, 04 April 2019 14:42
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Thu, 04 April 2019 18:19
		Re: A simple CP/M Z80 SBC without glue logic By: wsm on Thu, 04 April 2019 19:10
		Re: A simple CP/M Z80 SBC without glue logic By: etchedpixels on Fri, 05 April 2019 03:34
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Fri, 05 April 2019 05:44
		Re: A simple CP/M Z80 SBC without glue logic By: etchedpixels on Thu, 04 April 2019 09:49
		Re: A simple CP/M Z80 SBC without glue logic By: plasmo on Fri, 15 March 2019 09:03

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