Frequently I find the need to connect a BBC Micro or Master to the serial port on a PC. For example, to transfer files or other data back and forth. This ties up the serial port, leaving you with no spare port to connect other peripherals or communications equipment.
To solve this, I've designed and built a second serial port card for the BBC series of microcomputer, which simply connects to the 1MHz bus under the Beeb. It uses some surface mounted components so this circuit can't be built on stripboard but a PCB will be available instead.
More technical details are available on request, but a summary of the hardware features are:
a "pass through" connector so that you can continue to use any other 1MHz bus devices like the excellent MUSIC 5000 synthesiser or Teletext unit
uses the same serial chip as the main motherboard serial port which means excellent compatibility with existing software
receive/transmit rates independently adjustable between 75 and 19200 baud
compact 4.5" by 2.5" circuit running from 5V
all parts are easily available from Maplin or Farnell
On the software front, a ROM is available which is described in the User Guide present in advance on this issue's disk. It does all the talking to the hardware for you, as well as buffering.
You control the new port in exactly the same way as the main serial port, and a new command switches from one port to the other:
*COM2 (switch to the new card, use *COM1 to switch back)
*FX7,6 (set receive baud to 4800)
*FX8,4 (set transmit baud to 1200)
Blank, pre-drilled, double-sided plated through hole printed circuit boards will cost 20.00 GBP if ordered singly. The high price is due to having to recover the costs of tooling (a one-off payment I have to make). If over ten people buy a board, the tooling cost is spread thinner, though of course I don't know yet home many people will order!
If you need a kit of parts, or for the board to be assembled, please contact me separately for a price. If you want to buy a blank PCB, please contact me to reserve a board, and by EUG #59 we'll know how many people have ordered (or not!) and if it's economical to go ahead...
1st May 2001