Hi Mark!

In message <Pine.SGI.3.91.961220194631.12411C-100000@physig4.ph.kcl.ac.uk>
          Mark Brinicombe <amb@physig.ph.kcl.ac.uk> wrote:

> I have seen this problem recently but could not find a cause.
> The indication was that the driver was hanging up waiting for the serial 
> chip.
> What happens is when you open it it will try and clear the serial FIFO etc.
> sometime I found that no matter how many bytes were read from the serial 
> port the status register indicated there were still bytes present.
> As only I appeared to be experiencing the problem I had decided that this 
> was probably a hardware fault with my machine.
> 
> I'll have another look at the problem.

Well I start to remember that the German magazine c't reported problems with
the FDC37C665. It was quite a long time ago. I looked it up, it was 6/94.
Revision A to D of the chip won't remove chars in the databuffer if they are
present when the port is switched to FIFO mode.
You can get something in the buffer if you switch the modem on after the
machine which may then send an impulse to the chip.

I don't know how you can tell which revision of the chip you have and whether
any of the broken ones were used in the RiscPC at all.
Mine reads: SMC (R)
            FDC37C665GT
            A9429-B247
            6M73522-3
Well 9429 is the week when it was manufactured. As I don't have problems,
broken chips will probably have to be older than mine.
I don't think GT contains the revision as the chip on the photo in the c't
carries FDC37C665QF P.

Hope this helps,

Markus