Date   : Wed, 15 May 1996 21:04:57 +0100
From   : Mike Tomlinson <mike@...>
Subject: Re: BBC <-> PC connexion, the final message

In message <174@...>, Keith ELMO Eldridge <elmo@...
uk.net> writes
>
>
>Remember on the The BBC the domino (5 pin DIN) plug can be inserted
>TWO ways, which effectivly swaps Data In with CTS and RTS with
>Data Out. 

If I remember right, this was an unfortunate mistake on Acorn's part.
The original intention was to wire the port so that turning the plug
through 180 degrees reversed Data In and Data Out, and CTS and RTS,
therefore being able to try DTE and DCE wiring configurations just by
turning the plug, and not having to use a breakout box or get out the
soldering iron. But they got it wrong.

For instance, you could have used the same cable for a terminal and
printer, just by turning the BBC end of the plug thro 180 degrees. A
good idea, in principle!

Now, here is my tried and tested configuration for the BBC to PC lead.
This works fine transferring Xmodem files both ways, and also using
Kermit (which I can happily recommend).

Note that, unlike one poster suggested, I have had no problem
transferring large amounts of data at 19200 baud. The BBC user guide
does say this baud rate is not guaranteed, however.

I used the BBC serial port to create a pseudo-filing system for the
Spectrum. Sinclair's Interface 1, which had a serial port, was able to
save and load basic and machine code files through the port like a
normal filing system (Load *"b" and Save *"b" for those who remember). I
wrote a program to store Spectrum files on the BBC's disk drive via the
serial port and present them as a menu for loading back into the
Spectrum. The limitation was on files larger than about 20k, in which
case they had to be streamed from disc, which was very slow. Smaller
files fitted into the BBC's memory and were simply copied to the serial
port, which worked remarkably well. Oh, happy days.

Anyway, here is *the* cable pinout!

BBC domino serial, *looking into socket*:

     A  *     *  B

         C *

     D  *     *  E

A is RTS
B is data in
C is 0v
D is CTS
E is data out


Connect A to PC's Dsub9 pin 8
Connect B to PC's Dsub9 pin 3
Connect C to PC's Dusb9 pin 5
Connect D to PC's Dsub9 pin 7
Connect E to PC's Dsub9 pin 2

If you need to connect to a 25 way serial port I suggest you follow the
above and use a standard 9-25 converter. I have done this with success.

Not sure whether this matters in this context, but I connected the
shield of the two plugs together using the braid of the cable. This
would be important for long cable runs.

I have used cables of about 40 metres with no problems.

-- 
Mike Tomlinson
constructive email to mike@...               ; flames to /dev/null.