Imagine if Commodore
Posted: Sun Jan 07, 2018 5:37 pm
had scratched off the part numbers from all the chips on the VIC-20, and didn't publish the full schematics for us to use?
Yeah, terrible, right?
Yeah, terrible, right?
The Commodore Vic 20 Forum
http://www.sleepingelephant.com/ipw-web/bulletin/bb/
http://www.sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?t=8833
Be careful there. You may be in for a 'paternity' test!norm8332 wrote:I was previously thinking of designing and releasing the PCB etc. to PD for one like that with the 128K chip but I was going to use 74xx chips since I have a lot of those.
Had overlooked that detail so the BOM total price tag is around 1.50$. No wonder you'd want to scratch off the part numbers.norm8332 wrote:That link is for qty 10 GALs.
Good advice. But if for some reason you have too (like availability), I recommend using eBay because you can file a claim if there is an issue and the buyer always wins. I once got a RIOT chip for a Atari 2600 from a Chinese seller and it was the real thing. Also got a great deal on a couple authentic VIC-1 chips (6560-101) a few months ago.Floopy wrote:I only buy passive components from China. NEVER EVER buy IC's
I just want to be safe so that's why I just use Mouser and Digikey now. Sure it might be more expensive, but I get what I paid for!norm8332 wrote: Good advice. But if for some reason you have to (like availability), I recommend using eBay because you can file a claim if there is an issue and the buyer always wins. I once got a RIOT chip for a Atari 2600 from a Chinese seller and it was the real thing. Also got a great deal on a couple authentic VIC-1
Oh and just forget about ordering op amps from Chinese vendors I made the mistake on two occasions and both times the frequency performance of the amps was trash..worse than the ancient 1458 dual op amp no matter the markings.
That's why people ordering M27C512-90B6 ICs from eBay thinking they'll get a good way to make a cheap PLA sub actually get crap which only generates garbage.norm8332 wrote:... All of the Chinese-sold EPROMs are re-marks, I once ordered 27c64s and received chips marked 27c64 but they were actually the non CMOS 2764A variety. I didn't file a claim for the EPROMs because I expected re-marks at the price and they work fine.
If MC Scratchy is so concerned about his "paternity", he can scratch all the traces off the board, that works too.groepaz wrote:somehow seeing ppl arguing over this trivial stuff is cute <3
The PLA is a Programmable Logic Array. It's different than an EPROM. But an EPROM can act as a PLA in some cases. It is best described here: https://en.wikipedia.org/wiki/Programmable_logic_arrayFloopy wrote:The PLA is an EPROM?
Advantages over read-only memory (ROM)
The desired outputs for each combination of inputs could be programmed into a read-only memory, with the inputs being loaded onto the address bus and the outputs being read out as data. However, that would require a separate memory location for every possible combination of inputs, including combinations that are never supposed to occur, and also duplicating data for "don't care" conditions (for example, logic like "if input A is 1, then, as far as output X is concerned, we don't care what input B is": in a ROM this would have to be written out twice, once for each possible value of B, and as more "don't care" inputs are added, the duplication grows exponentially); therefore, a programmable logic array can often implement a piece of logic using fewer transistors than the equivalent in read-only memory. This is particularly valuable when it is part of a processing chip where transistors are scarce (for example, the original 6502 chip contained a PLA to direct various operations of the processor[2]).