12 Mar
2007
12 Mar
'07
12:42 a.m.
On 12/03/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Having had a quick squint (well it is 7am) at the beeb schematics, I'm
pretty sure it was changing S28/S29 - these alter the inputs to IC42,
a 74LS164 4 bit counter, used as a divider on the clock input to the
Serial ULA The only referance to these I can find online now is that
you can alter the cassette from 1200 to 1300 baud using them, so that
sounds like it's the right place. It was definitely a "change the
jumper(s) and set to x baud rate and it'll actually do y". It may
not have been the exact rate, but it was close enough that it was used
on a dial up to a 110baud port with no problem. (The dial-up used
totally dumb modem normally used for 300bps...)
Rob
I am fairly sure I persuaded a beeb to do 110 once, for dial-up to a
cetain university to play MUD.. I think it was as simple as changing a
jumper over, but this was about 25 years ago and so i forget exactly
which one.. It was certainly a non-permenant mod..
I wasn't aware of any such jumper... The baud rate generator in the Beeb
is inside the Serial ULA (the acutal serial chip is a 6850), and I didn't
think there was any way to get that to generate the appropratie output
frequency.