Date   : Fri, 10 May 1996 11:07:38 BST
From   : pt@... (Paul Theobald)
Subject: Re: How to make Beeb 2 PC cable

> 
> 1. Buy a PC to PC serial cable. This one has probably already
>    wired the different PC ground pins wired together at each
>    end, so I don't have to worry about that. (Or am I wrong
>    in assuming so?)

Possibly, though remember there are two different sorts of serial
cable out there, one for connecting between PCs and modems and
one for connecting between two PCs.  The latter will be wired up
to cross Data In/Data Out and the control signals.

> 
> 2. Remove one of the sockets from the serial cable carefully
>    writing down to which pin each wire is connected.

You'll need to examine both ends of the cable to make sure the
connections are as expected (see point above).

> 
> 3. Get a 5-pin domino DIN socket.

Yup.

> 
> 4. Connect the wire that used to be connected to the removed
>    socket's CTS to the DIN socket's CTS.
>    Same for RTS, Data In and Data Out.

The BBC's usage of CTS and RTS are (arguably) different from the
industry standard (ie PC) RS232 usage, and in fact more closely
follow that of DSR/DTR.  There is a good discussion of the
differences and similarities of each system in the New Advanced
User Guide for the BBC et al.  Note that the 'old' Advanced User
Guide gives some misleading information.

> 
> 5. Transfer Killer Gorilla!

Good luck!

> 
> Now my questions:
> 
> 1. Does the above procedure seem correct?
> 

See comments above.

> 2. The new wire-up would be:
> 
>    PC:                              Beeb:
> 
>    ground pins wired together        ground pin
>    CTS      <--------------------->  RTS
>    RTS      <--------------------->  CTS
>    Data In  <--------------------->  Data Out
>    Data Out <--------------------->  Data In
> 
>    Is this correct? (In particular: given that the Beeb's got
>    five pins and four of them are non-ground, there's only
>    one ground pin left. I cannot wire this up to something.
>    Or do I have to connect it to the PC's ground pins?)

I am currently using a different wire-up, albeit between a BBC
and a RiscPC, (which I believe is pretty similar, if not 
identical to a standard PC's interface) which was arrived at
after much referring to manuals and several hours of
experimentation.  There may be other equally correct solutions.

It is:

     RPC                    BBC

   1 DCD <---+
   2 RxD <---|------------> TD  3
   3 TxD <---|------------> RD  2
   4 DTR <---+------------> CTS 2
   5 0V  <---|------------> Gnd 1
   6 DSR <---|------------> RTS 5
   7 RTS     |
   8 CTS <---+
   9 RI

> 
> 3. Is TxD/Transmit the same as Data Out?
>    Same for RxD/Receive and Data In?
> 

Yes.  But watch out for CTS/RTS which are not the same on
the two machines.


In case anyone's interested, I have a short BBC BASIC program,
which can run on each end of the connection to transfer files 
(the same program runs on both the BBC and the RPC).
Mail me if anyone would like a copy.

Paul.