Search found 398 matches

by lance.ewing
Fri Mar 06, 2020 12:06 pm
Forum: General Topics
Topic: Happy 40, Vic!
Replies: 23
Views: 5476

Re: Happy 40, Vic!

4 colors per char. Maybe not 4, but 2 is something I was thinking of. What if the colour RAM were 8 bit instead of 4 bit, and what if the VIC chip had 8 pins dedicated to fetching from the colour RAM, where 4 feed into the foreground/mode as normal and 4 into the background. That obviously wouldn't...
by lance.ewing
Fri Mar 06, 2020 11:35 am
Forum: General Topics
Topic: Happy 40, Vic!
Replies: 23
Views: 5476

Re: Happy 40, Vic!

Sounds like a fun emulation project :D :D Why only emulation? :-) I guess because this might be something I personally could achieve by the end of September. My VIC 40 specs are limited enough that it might only take a few tweaks to an existing emulator. The biggest effort might be hacking the ROMs...
by lance.ewing
Wed Mar 04, 2020 11:35 am
Forum: General Topics
Topic: Happy 40, Vic!
Replies: 23
Views: 5476

Re: Happy 40, Vic!

Someone must put together a Vic-40 I guess if someone were to do this, we're most likely thinking of a couple of things: * 40 columns of text * 40K RAM as standard For the first, it implies using the 6562/3 VIC chip, which I think means double the clock rate for everything. And since 40 is double 2...
by lance.ewing
Mon Mar 02, 2020 11:32 am
Forum: General Topics
Topic: Happy 40, Vic!
Replies: 23
Views: 5476

Re: Happy 40, Vic!

The Brian Bagnall book mentions it as well, as follows: In late September 1980, the VIC-1001 debuted in the Seibu Department Store in downtown Tokyo. Seibu was the Japanese equivalent of Bloomingdales and sold high-end products on several large floors. At the time, the store hosted a computer show e...
by lance.ewing
Sun Mar 01, 2020 10:29 am
Forum: General Topics
Topic: Happy 40, Vic!
Replies: 23
Views: 5476

Re: Happy 40, Vic!

Does anyone actually know what day the VIC was released? I like to mark these days on my calendar (seriously). I couldn't find the exact date in 1980 that the VIC-1001 was released, but all the sources I've found that mention the Japan release say that it was in September 1980, at a department stor...
by lance.ewing
Wed Sep 25, 2019 2:35 pm
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

So tu sum up, with SR=0 on power up, the first shot of the waveform (e.g. POKE 36877,255) is identical to the real VIC20. But once you turn the voice off and on the two diverge as you can see from the picture below: ... A totally different result is when hypothetically SR is 255 on power up: the tw...
by lance.ewing
Sat Sep 21, 2019 5:16 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

I had to initialize the 8 bit SR ("noise_sg_sreg") to "11111111" at power on, otherwise the values produced are totally off when compared to the real VIC 20. Now I wonder, is it valid to assume the register flip flops are initialized to "1" in the VIC 20? (e.g. some we...
by lance.ewing
Wed Sep 18, 2019 4:15 pm
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

I haven't checked it rigorously (it's late), but a quick visual inspection shows they are indeed identical!!! :D :D :D and btw, it seems that the edge trigger solves the "timbre" effect as well ! (I will check it more rigorously tomorrow). I'm looking forward to seeing the result of the r...
by lance.ewing
Wed Sep 18, 2019 2:58 pm
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

yes the change in timbre is almost surely due to certain patterns stuck in the SR. The matter is HOW it gets stuck, because on the three sound voices the SR quickly fills with "0" after the voice has been turned off. Instead the SR on the noise voice seems to never gets cleared. The other...
by lance.ewing
Wed Sep 18, 2019 2:23 pm
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

I've just been doing some simulations, and it appears to me that the trigger for the 8-bit shift register is edge triggered and not level triggered. So that link from the LFSR, i.e. NSR0 (first bit), will only trigger the 8-bit SR shift when it goes from low to high. If I leave it on high, I can clo...
by lance.ewing
Wed Sep 18, 2019 12:55 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

So looking back at your last few posts, are we saying that it appears that the LFSR is shifting at the correct speed when the CR-D increment speed is twice CR-C's increment speed, but the 8-bit SR is then shifting twice the speed it should? Interesting. I will have to take a close look at the connec...
by lance.ewing
Tue Sep 17, 2019 3:15 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

What do those same three graphs look like for your FPGA implementation?

I've tried looking for a difference in the part of the 8-bit SR that rols back to the first bit, but to me they look the same when comparing noise vs non-noise.
by lance.ewing
Sun Sep 15, 2019 10:29 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

I'm afraid there is another glitch somewhere in our model. I sampled a POKE 36877,255 and performed auto-correlation of a small slice over the whole recording. On a real VIC-20 the waveform loops every ~15.2 seconds. On our simulated model (FPGA): - with CR-D speeding same as CR-C, the pitch is cor...
by lance.ewing
Sun Sep 15, 2019 10:04 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

It seems to me the 8-bit shift register on the noise voice behaves differently respect to the ones on the three sound voices. According to my hypothesis such register is not cleared when the voice is "off" as it does on CR-A, CR-B, CR-C, but it runs free (ROLs) without inverting the feedb...
by lance.ewing
Sun Sep 15, 2019 8:27 am
Forum: Hardware and Tech
Topic: 6561 Die Shot Reversing Explorations
Replies: 289
Views: 120548

Re: 6561 Die Shot Reversing Explorations

ok, thank you for checking and glad to read you again! Mid-July to mid-September is often an offline period for me, due to a mixture of weeks of holiday, and participating in an annual JS game programming contest. There is another little but crucial detail I would like you to check on the die shot....