Date   : Wed, 13 Nov 1996 13:28:05 +0000 (GMT)
From   : sf4000@... (Steven Flintham)
Subject: Re: More Z80 co-processor questions

[I sent this, or thought I had, a few days ago. When it didn't appear I
had another look and I think the problem is that I sent it to
owner-bbc-micro@... instead of bbc-micro@...]

I've replied to all the people who sent messages to the list in
response to my question in this one message. If I've made any mistakes
in attribution etc then please accept my apologies; I don't think I
have though.

Mike Tomlinson <mike@...$> wrote:

> >c) Is there any way of `resetting' BBC BASIC when ESCAPE has been
> >disabled? What I'm getting at is that on the BBC, unless the programmer
> >was nasty and used *FX200,3 or similar, you could press BREAK safely and
> >just type OLD. On the Z80 this just gives a * prompt. I suspect there's
> >no way round this but I suppose there's no harm in asking.
> 
> How about *BASIC, followed by OLD? Whether you get your program back
> depends on whether *FX200,3 had been issued, and whether the Tube was 
> active at the time.
> 
> Presumably you are referring to programs run in the I/O processor and
> not in BBCBASIC (Z80)?

Actually I did mean BBCBASIC (Z80). Because I'm using a Master and can
enable/disable the Z80 via *CONFIGURE it doesn't seem to ever cause
problems when I'm using BBC BASIC (6502).

> [ED help snipped]

Thanks for this, I'll give it a go.

> Finally, Steven's mail arrived through OiT - shouldn't we be using the
> netcom mailing list server, or is there something I've missed?

[There were some other comments about this.] Sorry, I just used the OiT
address because that's what I spotted in the header of another message
on the list. Hopefully this message has been sent correctly.

Pete Turnbull <pnt103@...> wrote:

> > > b) How do you return from BBC BASIC to the CP/M prompt? I think *BYE
> > > worked, but I'm not sure it's the right way of doing it.
> 
> > I can't remember for sure, but have you tried *Z80 or *CPM? I know it
> > could be done with the Torch Z80 unit.
> 
> ISTR "*BYE" too.  But the BBCBASIC manual gives an example of using
> BASIC in a batch file, and says *CPM is the approprite command.  BTW, the
> Torch units and software are about as compatible with CP/M and Acorn Z80s
> as intel machines are with ARMs.

Thanks, I'll try using *CPM instead.

> >f) What's the clock speed of the Z80? I think it's 4MHz but I'd like to
> >know for sure.

Mike Tomlinson <mike@...> wrote:

> In message <9611091250.ZM565@...>, Pete Turnbull
> <pnt103@...> writes
> >Not quite.  Almost all Acorn Z80s have Ferranti ULAs, and they're not
> >particularly reknowned as dodgy.  
> 
> Well, I replaced several in the 6502, and some Z80, external
> coprocessors in my time at an Acorn dealer. The most common failure mode
> was refusal to boot when the external box was switched on - the Beeb
> would just sit and sulk with the cursor flashing in the top left hand
> corner. Replacement of the ULA cured the fault every time. The new issue
> ULAs - VLSI, AMD, whatever - were pin compatible by the time I received
> them.
> 
> There was a problem with some of the ULAs on the internal 6502
> coprocessor units on the Masters too.

Given this, if the problem seems to persist, how easy would it be to a)
obtain a replacement ULA and b) fit it (is it socketed and easily
accessible?)?

Thanks to everyone who replied; since I posted my message about a week
ago I was wondering if I'd somehow offended everyone with my last post
and everyone was ignoring me, but I can only assume that there was a
delay due to my not using the correct address.

Steven