BBC Microcomputer Service Manual Oct 1985 Section 1 BBC Micro ...

7.3 Hardware Hints and Tips
Here are a number of miscellaneous hints and tips which have come from
various sources.
* RS423 at 110 baud
In order to get the RS423 interface to work at 110 baud, all that has
to be done is to use the *FX8,1 command in order to set 75 baud and
then change the position of link S28. This link is made by a track on
the PCB, between the centre pin and the west pin. This link has to be
broken and a solder link made from the centre pin to the east pin. This
has the effect of speeding up all of the baud rates, both send and
receive by 44%, and also makes the cassette port run fast by the same
amount, so a single pole double throw switch could be wired to S28 in
order to select the normal speed or the fast speed for the 110 baud.
The actual speed produced is 108.333 but this is near enough for most
teletype printers.
* Disabling Break
For certain applications, particularly when the computer is being used
by very young children, it is most frustrating when the user presses
the break key. It is easy enough to disable the escape key within a
program, but the break key is mare of a problem. You could use *KEY10
OLD|M RUN|M but even this is not very satisfactory. The alternative is
to disable the break key electrically, which can be done by removing a
link from the keyboard PCB. You could then wire it up to a miniature
ON-OFF toggle switch which can be mounted on the back of the case by
drilling a suitable hole, or leave it open circuit and use the contacts
at the back of the main PCB marked "RST SW", to provide an alternative
break key. The disadvantage of doing this though is that if you are
using a disc system, you may want to be able to do a SHIFT break in
order to boot the disc. The position of the link to be removed is shown
below.
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