Testing a Z80A with a logic probe

[hungar]

Hi all, I'm pretty new to this logic probe business and I'm trying to test a Z80 thats in charge of sound duties. I've been going through the Z80A manual testing the pins to see if they match up (high Low, tristate etc) and a few of the pins don't seem to match and I wondered if that suggested a fault or if they are just finished with their job.

BUSACK/RFSH and BUSREQ the manual says active is low. They are pulling high.

IORQ output, active Low, tristate. This is pulling high and pulsing.

INT input, active Low. This is High/low pulsing.

I'm very much in ignorance corner here so please excuse me

Thanks!

hungar2017-04-19 21:43:05

 

[ArcadeHacker]

Active low means they will be low when "used/activated". It doesnt mean that they need to be low all the time, their resting mode is being high. The opposite scenario applies to non active low signals (the ones not referenced with a "/" symbol)

 

[andrewsm]

All what you describe here is correct however testing a Z80 with a logic probe will not reveal very much information only in that it is active or not. From what you have observed, I would say that the Z80 is running but you have no method to tell whether its reading the code correct or not. BUSRQ will usually be high as it hardly used in arcade boards. The other signals pulsing high or low simply indicates activity which would be normal. This also suggests the clock is ok and something is happening, If the sound still does work then it could be a variety of reasons which a logic probe wont really help with,

 

[hungar]

Wow thanks for the replies guys.

So theres a good chance the Z80 is ok, I have audio coming from the YM chip its just the sound effects that aren't playing. The main amp and the opamps connected to the Sound and FM output seem to be functioning.

Looking at the schematics am I right in saying that I could check other components connected to the address and data bus and I might possibly find something?

< ="chrome-extension://hhojmcideegachlhfgfdhailpfhgknjm/web_accessible_resources/index.js">