Re: 128CR (fwd)

From: Nicolas Welte (
Date: 2000-01-29 13:22:15

Raymond Carlsen wrote:
>      The 40 column is the NTSC standard 14.31818 Meg and the 80 column is a
> single (two wire) type, unlike the flat USA 128 which is a 4 pin. This
> crystal has solder on top covering some of the writing, but it appears to
> be a standard 16Meg "16000 KD..6C". I noticed that my USA 128DCR doesn't
> have a crystal in the RGB section, but there is a 16M crystal in the area
> of the drive controller of that motherboard.

Yes, the DCR has only one 16MHz crystal: It is connected to the 5710,
which then puts out a proper 16MHz TTL clock. This signal is then also
routed to the RGB chip. The plastic 128D had the luxury of two separate
16MHz 4 pin oscillators: One in the video cage and the other one on the
separate drive controller.

I guess in your 128CR it's done this way: The 16MHz crystal is connected
to the second 8701 which is only used to generate a proper 16MHZ TTL
signal on the Phi(color) output which is then directly fed into the
2568. The dotclock output probably isn't used at all, maybe that circuit
is even disabled. Can you check the outputs of that 8701 with a scope
and tell us the levels/frequencies on each pin?

>      One other thing I just noticed about this C128CR motherboard is that
> the footprint is slightly smaller than my flat 128 motherboard. Although
> the connectors on the right side and rear line up exactly with a flat 128,
> the left side and front of the board have about 3/4" trimmed off, so the
> mounting holes would not line up if I tried to install this board in a flat
> 128 case. Otherwise, it fits fine.

Maybe they planned to add additional mounting points to the case, just
like they did for the VIC20CR and the C64E. I'll sometimes have a look
at a few C128s, I also have a late one with rev 9 board and see if it is
already prepared for the CR board.

> I'll try that, but I don't know what kind of quality I can expect since the
> board doesn't sit flat against the table. I've never tried to scan a 3D
> object. I have an older digital camera that I can try too. If that's not

It depends on the scanner, I usually get very good results with various
PCBs on a very cheap scanner. 

> image, I'll send it along. By the way, I don't know if Marko reads this,
> but if you think he would be interested, please let him know. Thanks.

I'm sure he'll read this on the list, and the pictures can probably be
stored on funet somewhere. And if Cameron reads this, he will be dying
to get a copy for Secret Weapons ;-)

> > Just looked, the service manual has another view of this, it is not
> > clear to me whether the two chips are the same or above mentioned
> > differences apply. But a CMOS version is listed in the SM.
>      Is the information important enough for me to try a 8568 in that
> board or the 2568 in my flat 128? How much risk?

I don't think anything will get damaged, but it's not necessary to try
this. Just track the 16 MHz clock signal, if it is generated as I think
(by the second 8701) then it should be a plain TTL signal.


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