When I first left the world of corporate employment to start my consulting
practice, I met a small company with five or six employees, most of them
founders, that had written software to integrate bar code readers and IBM-PCs,
and I do mean the original 8086 PCs. They had begun to sell and install their
product into mature manufacturing plants that were beginning to automate their
operations.
My new client was purchasing an external box that connected four RS422 lines
to one RS232 port in the PC. This type of box, called a multiplexer, required
the application software in the PC to send special codes over the RS232 line to
select which RS422 line to connect to the computer. They asked me to design a
peripheral board, which would be installed in the PC, to replace the
external box. I designed the hardware and built a wire-wrapped prototype board.
The board interface with the PC was identical to a serial communications board,
and therefore did not require a custom driver.
My client was pleased with the prototype and hired me to develop and
manufacture the printed circuit board. This project saved my client money in the
long run because the boards were significantly less expensive than the external
box.
As now, computer technology grew rapidly in those days, and after a year or
two, this product became obsolete when true multi-port communications boards
became available in the general commercial market. But in the meantime, my
customer had found a cost-effective alternative to purchasing the multi-port
communications they needed for their product.
