On start-up you should get some activity of /SEL F and /SEL E signals. Study your scope and learn how to set it up for 'single trigger' mode. Sync the scope to Channel 1 and connect channel 1 to /SEL F. Connect Channel 2 to /SEL E. Use your PET reset button to start the test. See if you capture pulses on both scope channels.
The SELECT signals can be found on sheet 1 on UE12 (74154) which is a 24 pin chip. /SEL F is on pin UE12-pin17 and /SEL E is on UE12 -pin16.
/SEL F selects the kernal ROM and /SEL E selects the EDIT EPROM that holds the PETTEST V4 code.
-dave_m
Good afternoon/evening....
OK sad news... the scope I have is not able to be set to do a "single trigger" - it has a lot of entry level features but that isnt one of them... I have tried all sorts of different settings with zero success....
The Logic probe I have, I have placed on Pin 16 and 17 of UE12.... Pin 16 stays HIGH, while Pin 17 stays LOW....
With the scope I have, I am unable to detect or meansure any pulse or activity that is clean.... in testing the probes, they are calibrated properly and read accordingly during the calib...
So, I can either deduct that the SN74154N is bad (aka UE12) or I just don't have the proper test hardware to get a proper reading....
As for the EPROM, the burner I have is a GQ-4x4.... its able to burn chips, but the software that the company has produced works in a windows enviroment.... everytime I would attempt to run this on my mac using either Parallels or VMWare images (WIN 7 or XP) - the burner software would crash. I was able to duplicate this on a straight XP Windows PC (seperate laptop) - the company replied to my trouble request, and stated the internet needed to be disconnected from the laptop before starting the software....
Now, it works, but in order to get the EPROM image to load using their software, I have to load the image first, then set the "offset' before selecting a chip to burn.... otherwise, their software states the "image is too big to fit on the chip" and then truncates the software (which I figured out the .bin files and .hex files were starting at the address that Dave mentioned above at $E000, but this software for the burner defaults to address 000000 and was deleting anything beyond what it thought the EPROM could store... I have not yet perfected the use of this software yet, but I have a few things to try)
But since the PET doesn't seem to be talking to any of the EPROMs, burning the PETTEST isn't going to get me very far.... I will need to see what else might be going on .... I can obtain another SN74154N chip from a few different suppliers...
so......... here I am LOL
Thank you guys for being patient with me on this one....
Rich