On Sun, 18 Apr 1999, [ISO-8859-1] Marko Mäkelä wrote: > On Sun, 18 Apr 1999, Nicolas Welte wrote: > > > The early 6567 chips also had a different timing that looks like it was > > made for exactly 1MHz system clock. > > Yes, and the VIC-10 a.k.a. UltiMax actually has two crystals: 8 MHz for > dotclock and 14318181 Hz for color clock. All 8-bit Commodores I have > seen contain only the color clock crystal, and the dot clock and bus clock > are derived from this crystal. The factors are as follows: > > VIC-20 C64/C128 > PAL 17734472/16 17734472/18 > NTSC 14318181/14 14318181/14 > > > This is also the clock frequency of the Ultimax computer which uses a > > 6566 VIC-II chip. > > Oh, there you said it. :-) > > > It's a pity that you don't have your original C64 anymore. There's > > always the search for early chips to explore funny bugs. I think Andreas > > Boose wanted to know once if the reset bit, that is disabled in all > > known VIC-II chips is perhaps active in very early versions. Perhaps you > > could try it on your machine? > > Funny that you had the same thought as me. > > Also, I forgot to suggest in my previous message that maybe someone who > has built an adapter for reading the contents of 82S100 PLAs could read > out the truth table from the early PLA. I don't think that there will be > any differences; I'm only suggesting this just in case. I do not have the equipment to read the actual logic terms. I have constructed an adapter that reads a PLA as if they were a ROM, that is, the sixteen input lines are addressed as address lines, and the 8 output lines are read as 8 bit data. Using this adapter, I have read the actual output of a number of PLA's for every possible combination of inputs. This creates a 64K file. Every PLA I have read has produced identical output. This includes some early PLA's with paper labels. Unfortunately I have not kept a record of the label numbers. It did not seem to be useful as the results were identical. It skould be noted that because the output is identical, does not mean that internal logic terms are identical. There are a number of different ways of programming the PLA that are logically equivalent. In fact, there is no unique truth table for this PLA. There are a number of ways of representing the output of a PLA this complex, that appear quite different when presented as a truth table, that are logically equivalent. Bill - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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