Adam Smith <adam@VIRATECH.COM> wrote:

> What is special about the number 3.6864 MHz?

It happens to be 230.4 kHz x 16, which means that you can generate
all the standard baud rates using simple divide-by-2 and divide-by-3
stages. Very commonly used with early baud rate generator chips.

One trick I learned long ago is that you can approximate this frequency
pretty closely if you have a 16.000 MHz clock source. You need to set up a
"multiply by 3/13" circuit, which produces 3.6923 MHz, off by just 0.16%.

It's simpler than it sounds: You just need a 4-bit synchronous counter
(such as a 74LS161) set up to divide by 13 (load with 0011 when it gets to
1111), and then use the "B" output, which gives three pulses for every
group of 13 input clocks.

-- Dave Tweed

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