*** M E M O R U M ***

Did you know the Z80 has two types of reset, normal and special? No? Well I didn't either until last month. An in-depth study of the Z80 special reset has been completed and please click on the link below for full details.
http://www.primrosebank.net/computers/z ... _reset.htm

If you were wondering why Dave has been a bit quiet lately he's been slaving away doing special reset tests. Many thanks Dave!

I did wonder how the IDE worked. I presume (not found time to read up yet) it uses the Special Reset.

Somewhere in a technical question and answer section, Zilog say that really, the external control inputs should be considered to be synchronous (I think Reset was one input that was being referred to). Now we know why

So thanks for supplying this information

BTW, how did you start looking into this? What sparked the search?

Mark

It's the Z80 Family Questions & Answers (http://www.z80.info/zip/ZilogProductSpe ... 29-143.pdf) that says /INT, /NMI, /BUSREQ, /WAIT and /RESET should be synchronized to the system clock and /INT and /RESET certainly were in the special reset logic (other signals not needed).

It was finding out about the patent that sparked the interest in the special reset. One thing I didn't mention in my report is that for 1T and 2T normal reset pulses it takes 3T from last rising edge of clock when /RESET is low to start of fetch from address zero, which is exactly as specified in the databooks, which is why I didn't mention it!

Something not tested was NMI and special reset. If /NMI goes low when /RESET is low during a normal reset the CPU does not ignore the /NMI signal and it will be accepted at the end of the first instruction after the reset.