From: zzyyzz@mixcom.com (Vincent Mulhollon) 
Subject: Re: Z80 Reset question
Date: 1 Jun 1996 01:38:36 GMT
Rocky (suesound@iafrica.com) wrote:
: Maybe you could use the /BUSRQ signal - that definitely causes the bus
: to be released. I think /RESET does not tri-state the /WR & /RD lines but
: /BUSRQ does.

 "The Z80 microcomputer handbook" William Barden, Jr, 1978, page 29 says:
"When /RESET is brought low, the following actions occur:
<SNIP>
5. The address bus goes to a high-impedance state.
6. The data bus goes to a high-impedance state.
7. All output-control signals go to the inactive state."
So "Rocky" is right.  /WR and /RD go high, NOT high-z.
Might I suggest OR logic for the /WR and /RD with a few invertors and stuff?

Of course, /BUSRQ will actually do what you want.
  Extra credit for you if you implement handshaking with the /BUSAK signal.

Vince Mulhollon N9NFB