Moderator: Moderators
Your problem appears to be your trigger setting and you're not saying what signals we're looking at here.
I am mystified as to how you can come to this conclusion. I have no idea what I am looking at.It does show that the loading is not quite right. Could be the capacitive load from the veroboard?
I can assure you the heat sink is totally unnecessary.
CASRAM is probably a line you should just avoid because on the vast majority of C64 boards, there is an RC filter to slow down the rise/fall time on this specific line to give time to the multiplexers to do their job. It's a very unusual impedance loading that doesn't exist in 'normal' land'.This is the /CASRAM output Top trace is in-circuit bottom trace 10k pullup loaded.The data sheet for the hitachi 4164 says that the CAS has a 10pf input capacitance and as the PLA drives this directly there is an 80pf capacitance on that line. I can only assume that it is to ground, There is no mention of resistance though but as the trace is showing a slower rise I am assuming that 10k pullup is not enough. I think i will have to work through individual loading of each line to get as close as i can to the correct output before testing some replacements.
The trigger should always be at TTL level or about 1.3-1.5v.i have tried adjusting the trigger level but it goes to the point of being so dim as to be almost invisible and still has ghosting .
Your scope is analog and gives you the illusion you have 'normalized' them. I reality, what you see is different activities superposed because your scope can't provide you with a single capture. The 'good' capture which is representative of what's really going on is the one you consider 'wrong' or 'not normalized'.
I assume when you say compare the 'timing', you mean the response speed to a given input. To do that, you must use a fully digital oscilloscope and since we're talking nanoseconds in difference then yes, a 100MHz scope will definitely help.remember i am trying to compare the timing on 2 PLA's ( or PLA and substitute ) at the same time so getting signals from elsewhere is a definite no go.
You're joking, right ?
You cannot do what you want to do with an analog scope... at all !I will have to do what i can with what i have.
That's incredibly inexpensive for what you want to do.
.That's a good piece of information with the results I am looking at in this folllowing video I made regarding the Winbond W27c512 EEPROM.
RMS ?? RMS is to measure the energy from an AC signal such as a power outlet or what comes out of an amplifier.banman wrote: ↑Sat May 16, 2020 10:08 pm I did note these following results are taken with the oscilloscope talking readings from a powered off to powered on C64.....
OTP PROM marked CHINA the RMS voltage on pin 10 is around 240mV (I did notice that this chip did not trigger eslapion's glitch tester on startup- this is a significant observation)
Commodore Factory PLA RMS voltage on pin 10 is around 3.5V
The Ultimate PLA RMS voltage on pin 10 is around 3.75V
Original ST PLA (From electronics shop) RMS voltage on pin 10 is around 3.5V
Texas instruments UV EPROM PLA RMS voltage on pin 10 is around 4.5V
Winbond w27c512 PLA RMS voltage on pin 10 is around 4.5V
I am not sure on these RMS voltage readings. I think the big RMS voltage reading is a fact that the oscilloscope is taking the values of an off C64 to an on C64. Someone may be able to shed some light on this issue.
Now you're talking! You're using a digital scope and you've nailed it. A clear notch down exactly where it shouldn't be. This PLA replacement causes problems and you've clearly identified it. This is what triggers the 74LS279 detector.
Which means they fall below the 1.5V TTL level threshold and will cause problems.I noticed that the minimum voltage got to 860mV and below.