Asynchronous Communications Interface Adapters

The RC2014's Serial I/O module and the Dual Serial module
(using Zilog's SIO) both have an important shortcoming: they
hard-wire CTS to ground. Considering that these modules' main
purpose are to communicate with a modern machine through a USB-
to-TTL dongle, this hard-wiring make sense: a modern machine
have plenty of power to take whatever is coming on a 115200
bauds channel.

However, this becomes problematic when communicating with the
RC2014 through an underpowered machine running Collapse OS:
RTS/CTS flow control doesn't work.

For this reason, I recommend that you build your own ACIA
module. A schematic for it is in img/acia.jpg. This module is
exactly the same as the "official" Serial I/O module, with two
differences:

1. Wire CTS properly
2. Add a '393 counter to allow for lower baud rates.

This design with the '393 has an important limitation: you can't
easily fine-select your baud rate. For example, dividing by 12
(for 9600 bauds) is not straightforward with a '393. However,
because the '393 is a dual 4-bit counter, it can divide more.

You might want to replace the '393 with a '161 with preset if
you want to divide by a more specific number.