Saturn Modchip help

I can't seem to find the any info on the SSB-03 modchip, I'm trying to find out where the signal point is for the modchip. I also have a Sanyo 610-6473-30 drive if that makes a difference.

 

I think the SSB-03 is one of those designs that just has two chips, the PIC and a PAL? If so, try wiring the clock to pin 6 on the PAL. That's generally where the 8.4MHz goes.

 

Yeah, it's only 2 chips. I have no idea what the pin 6 would be.

 

The looks like it's set up to get the clock from pin 1 (the 33MHz clock signal from the main board). If you want to use an external clock, you have to cut a trace before soldering on the wire.

Test it first, since it may well work just as it is.

 

Thanks, I'll check it out tomorrow.

 

It doesn't seem to be working on my sanyo drive. it works fine on my american saturn but that one doesn't have a sanyo drive.

 

Sanyos don't play nice generally speaking. That chip works great in 64pin Saturns in my experience.

 

Yeah, it works great in my 64pin saturn too.

 

x

 

You have said this repeatedly, but it's simply not true. They are not the same signal and they are different frequencies - to be precise, one is 4 times the other. To be more precise, it used to be 8.4MHz on the old drives with the on-board 33MHz xtal, but was switched to 33MHz on the later models.

These were taken from a Japanese VA11 board with an EXL-P608 drive S/N A8F040790

Upper: Pin 1 on ribbon cable

Lower: Pin 14 on the CD IC401

 

x

 

There is no signal point, the 8.47 MHz clock is expected to be on the ribbon connector. Is that not the case with this Saturn? I'm quite positive the modchip isn't capable of dividing the 33.87 MHz clock itself so a couple of D flip flops or a synchronous counter is necessary. I'd go with a 74AC(T)161 in case it's necessary to align the clock phase using another signal as reference (the modchips with their own oscillators get around this somehow).

 

x

 

You have BCLK, which is 8.4MHz most of the time (I have a feeling it drops down to 4.2MHz when playing audio CDs, though) - this is in it's usual place on pin 14 and also on pin 9 (physically connected together) Apart from the 33MHz clock on pin 1, that's the only stable clock on the connector, but attempting to use it as the replacement for the 8.4MHz that used to be on pin 1 results in flaky behavior. I'm not quite sure why this is - my first guess was metastability issues (since the PIC pins change of the rising edge of the clock in Q1 and it's the same signal that's being used to clock the PAL), but since inverting the clock didn't seem to make any difference I guess not.

The same machine and modchip is, however, entirely stable if you derive the clock from the 8.4MHz on pin 14 of the sub-CPU. No idea why. Possibly aliens.

edit:

OK, I just checked again, and the only way you can get 8.4MHz out of BCLK is when the drive has got confused. if the drive initializes properly, it sets BCLK to 4.2MHz and LRCLK to 88.2KHz (24 bit cells, x 2 channels), and then drops down to 2.1MHz (44.1KHz LRCLK, 24 bit cells) when it goes into audio mode. When you actually play the CD, LRCLK stays at 44.1KHz, but BCLK goes to 2.822MHz, presumably indicating a transition to 32 bit I2S cells. Under certain unclear conditions, I've also seen it step up to 5.6MHz while reading a Saturn disc.

This also means that the real mystery was why it worked even once, since it's the wrong frequency...

On this specific drive, the signals seem to be as follows:

1: 33MHz clock
2: GND
3: Drive status info
4: Drive commands
5: Command / status byte sync line
6: CD Frame marker - 60Hz in idle, 150Hz with Saturn CD, 75Hz with audio CD (
7: Command / status clock
8: GND
9: BCLK - Varies with drive mode, as described above
10: Pulses high at CD frame rate. Frame sync?
11: High all the time as far as I can see
12: GND
13: LRCLK
14: BCLK (same as 9, and wired together)
15: DATA (both CD-ROM and digital audio)
16: GND
17: Low with a CD-ROM, high with an Audio CD. Might be X1/X2 indication, too.
18: Looks like Q subcode
19: Looks like clock for 18
20: Normally low, pulses high during seeks and if you disturb the drive. Error flag?
21: Looks like clock for 20

I can't see anything that would be useful as a clock.

Edit again: after a bit more poking around, it looks like the 33MHz clock is fed into one of the Xtal pins on the MN662724 and the 8.4MHz comes out of pin 19 and then gets fed to pin 14 on the M37477.

 

x

 

So where would I put the signal wire then?

 

x

 

I feel like I'm missing something in this discussion. Do other Saturn models have a reliable 8.4 MHz signal on the ribbon that isn't BCLK? AFAIK you should be able to use BCLK directly for timing because logically that's what the GAL and PIC are synchronized to. It doesn't matter what the frequency is (as long as the PIC performs its lookup in time), or that it varies, because once the modchip performs the swap trick it goes out of system. The PIC is used as a state machine and ROM, and the GAL as a shift register, reload counter and multiplexer.

IIRC the GAL must invert the clock for the PIC because it's negative-edge triggered; the proper place to insert timing would have to be the GAL's pin 1 which is the only input that may clock its internal registers (note that pin 1 must already be connected to another ribbon signal, presumably BCLK).

If this modchip *is* already connected to BCLK and this Saturn's ribbon doesn't have a strange pinout or something, and it still doesn't work, then it's safe to say that the timing or protocol is different to other Saturns and trips up the modchip.

 

x

 

Yes, the older drives output 8.4MHz either on pin 9 (20 pin drives) or on pin 1 (21 pin drives) - this seems to have been used in place of the on-board oscillator to clock the PIC, while BCLK was used to drive the clock pin on the PAL. And not all of the chips just drop out of circuit - some of them (I.E. the cost reduced ones) don't have that mux and use the PIC to relay the command / status data (although the SDATA appears to be muxed in the PAL). On a practical level, trying to clock the PIC with BCLK on the board I'm playing with here doesn't work - half the time the Saturn won't even see the drive and even when it does it generally won't boot.

In practice, they seem to have had different clocks - either an on-board osc or the 8.4MHz for the PIC, and BCLK for the PAL. The board I have here seems to have been designed with an inverter in BCLK (it feeds into pin 2 of the PAL and then comes out again on pin 23, which is linked to pin 1), but the trace has been cut and pin 1 wired directly to BCLK on the ribbon.

The one I'm looking at is connected to BCLK, but also gets the 8.4MHz clock for the PIC from pin 1 of the ribbon cable. It works fine in an older model with the EXL-P605 CD drive, since that has the 8.4MHz MCLK on pin 1. It doesn't work on this VA11 board with the P608 CD because that same pin is no longer 8.4MHz. If you isolate the trace running to pin 1 and then connect it to some other source of 8.4Mhz, then the chip works.

Reads as 19.998Mhz, so I guess 20MHz is right. I also discovered something interesting about the signal on pin 1 - it is being generated by the Saturn, but depending on the state of pin 8 can output either 16.9 MHz or 33Mhz. This is based on the state of pin 8 - the JVC drive grounds it, which selects 33MHz and I assume the Sanyo leaves it open and gets 16Mhz.