ZX81 driving a SID 6581

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

Thanks Sir Morris!
After I added the inverter to my latch signal to make the /CS the circuit got funky. I suspect I need a pullup resistor. I went back and put in a transparent latch on the data and kept the edge triggered on the address. When you hit a Poke you can see the address lines show up and then the data. One would think it would be too fast for the naked eye. I need a long walk!

John
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

I put in a one shot that gives me a 8us pulse to the /CS. The circuit seems to be working. Just one more flaw! The address decoder starts putting out pulses if the ZX81 sits there not running for a few minutes. This is my second ZX81 that does this! Is this the Ghost of Sinclair? At this time I will hook the Address lines from the ZX81 straight to the SID. Place your Bets!
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Andy Rea
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Re: ZX81 driving a SID 6581

Post by Andy Rea »

crankorgan wrote:I put in a one shot that gives me a 8us pulse to the /CS. The circuit seems to be working. Just one more flaw! The address decoder starts putting out pulses if the ZX81 sits there not running for a few minutes. This is my second ZX81 that does this! Is this the Ghost of Sinclair? At this time I will hook the Address lines from the ZX81 straight to the SID. Place your Bets!
what do you mean by not running ? as in powered off, or do you mean just idle with the cursor waiting for some keys to be pressed ?

if it's the latter then something is a-miss somewhere as the address / data / control busses will all still be doing there merry thing..

if it'sthe former then you'll be needing pull-ups / downs on the control lines to your address decoder so that 'floating' inputs have no effect.

Regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
pastbytes
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Re: ZX81 driving a SID 6581

Post by pastbytes »

Electrically you should not have problems connecting the address bus directly to the SID, the actual problem with that is the Z80's speed, your pokes will last less of one 1MHz cycle and then the buses will change when fetching the next Z80 instruction, so unfortunately you need to latch both buses. I never thought that interfacing a C64 chip would be so complicated, the good thing is that when you make it work, you will have access to paddles and Commodore 1351-compatible mice, by reading the POTX/POTY inputs.
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

Andy,
After the program has been stopped and the cursor is just sitting there. It is about five minutes each time. Then my address decoder starts putting out pulses that cause the latches to put out data.

PastBytes,
My latches are one way so there is no paddle input! As for hooking the SID to the ZX81 I know how that can be done I was just doing it to prove that the SID requires certain requirements not like a Memory Chip. I just hooked the address straight to the SID. Just the addresses. It fires off sometimes!!!! A simple way would be to divide the ZX81 clock and redo the numbers for the frequency. That might produce off key notes. The best way is to phase lock loop a 1K oscillator off the ZX81 Clock.

While typing this the Ghost of Sinclair is running the SID.......Now it stopped!
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

Here is the TEST 64 program

10 poke 54272+int(rnd(1)*25),int(rnd(1)*256) : goto 10

54272 would be 8192 on my machine.
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

The one shot works! I also did a set/reset flip flop. The buffer latch signal goes to the flip flop. As it goes from high to low it flips the flip flop. The 1K system clock flips it back. That signal clocks the data into the SID (Synchronized with the system clock) Now the elephant in the room! ZX81 BASIC does not support DATA Strings. (Crashing sound of the whole project)

You see this?

10 poke 54272+int(rnd(1)*25),int(rnd(1)*256) : goto 10

Yea it might work on a emulator but on a READ 64 it sucks! Popping noises. My ZX81 running similar code does the same things.

Time to put the ZX81 back on the test bed and program in a song using just POKES!!!!
sirmorris
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Re: ZX81 driving a SID 6581

Post by sirmorris »

Glad to hear things are progressing. There are many 'data' substitutes available. REM lines containing strings of numbers and a subroutine to pull them out have been around as long ad the zeddy. I couldn't point you at one right now though; does any other reader have a link ?

C
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

Ok Sir Morris,
I will hunt the info down.

John
crankorgan
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Re: ZX81 driving a SID 6581

Post by crankorgan »

I have been tracking down the "Sinclair Ghost". Funny Huh? It shows up on my two ZX81s test board. The Ghost is coming from the output of the 74HC251. The 74HC251 only has four signals. A13 A14 A15 and MREQ. MY guess is MREQ is putting out signals every few minutes for about 60 seconds. Tomorrow I will do more testing. What ever it is it makes the SID play the same sequence of sound for about a minute and then it stops. Oooooooo Hooooo Hoooooo
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