Can you replace your C64 PLA for under $3?
180K views · Mar 14, 2020 · Science & Technology
Comments · 633
@danielmantione · 6 years ago · pinned
The reason why the PLAtinum fails is clearly that they have their CAS to CASRAM delay wrong. Later C64 boards uses a resistor+capacitor to delay CASRAM a little bit, and the modifications advised are intented to increase the delay on the mainboard side. Another solution is to replace the multiplexers on the mainboard with faster ones, if you replace the 74LS257 with 74ALS257 or 74F257, PLA compatibility problems are solved. I actually did this on a board with a broken multiplexer, not for compatibility (original PLA was working fine), but just because there wasn't a lot of reason to use the older, slower LS part.<br><br><br><br>As the creators did use a CPLD, they should have been able to route the signals through different macrocells to add delay, just like I was able to do, but they didn't. You need to dig a bit into the low-level details in order to achieve this, perhaps they didn't do this. For me it was't that hard at all to get the CASRAM delays right and I believe most PLA replacements do get it right.<br><br><br>The RAM in the C64 has to respond in something in the order of 250ns to the CPU. The entire chain of logic (PLA, multiplexers, RAM itself) has to happen within this 250ns. With 150ns RAM, there is about 100ns left for PLA/multiplexers. The lower bound is approximately 20 ns and this means there is quite a bit of range, the PLA isn't quickly too slow, even above 50ns you would still be on the safe side. However, modern chips are fast, so quickly get in trouble with the lower bound.
291
@kiningroseburg9288 · 6 years ago
<a href="https://www.youtube.com/watch?v=GKyoh_gGTYM&t=1379">22:59</a> "Boom! Blue screen! Looking good!!" Said no system administrator EVER!
146
@branchonequal · 6 years ago
BTW, the exact reason why the PLAs fail is because the glass separating the layers of the die contains too much boron which destroys the aluminum interconnections.
137
@ddummer · 6 years ago
"Boom! Blue screen... looking good!" ... those were the days long before windows... ;)
117
@copperdog01-i2o · 6 years ago (edited)
You might be able to talk to The 8-Bit Guy about testing the Epyx Fastload cartridge.
40
@quirin1727 · 6 years ago
Blue Screen!<br>C64 User: Yeah, it works! 👍<br>Windows User:😞
21
@StevenIngram · 6 years ago
I remember the old Pr1me mainframes. When 2 devices tried to communicate on the bus at the same time it generated an error code called, "Fatal Embrace." LOL
47
@jamesbennettmusic · 6 years ago
Cheap breadboards are brilliant for holding pin headers for soldering!
66
@dan_loup · 6 years ago
"oh yes, my computer bluescreened, which means it worked!"
69
@ThereIsOnly1ArcNinja · 6 years ago
Damn, it really took me over 30 years to realise, that we C64-afficianados prefer to get a blue screen - in contrast to Windows
7
@matthewday7565 · 6 years ago
Windows user - reacts with horror at blue screen<br>C64 user - blue screen is my friend
9
@osgrov · 6 years ago
This is awesome! Daniël deserves a medal, for sure. :)
29
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