Quiz

What is not a standard windows UART baud rate?

What is not a standard windows UART baud rate?

• 150 Baud
• 300 Baud
• 55 Baud
• 110 baud

EXPLANATION

It started a long long time ago with teletypes — I think 75 baud. Then it's been mostly doubling ever since, with a few fractional (x1.5) multiples, for example 28,800, where there were constraints on phone-line modem tech that didn't quite allow it to double. Standard crystal values came from these early baudrates, and their availability dictates future rates. E.g.,
$$7.3728MHz167.3728MHz64=460,800baud=115,200baud.$$

Most UARTS use a clock of $$2n×16$$
 of the baudrate, more modern parts (e.g. NXP LPC) have fractional dividers to get a wider range by using non-binary multiples.
Other common standards are 31,250 (MIDI) and 250K (DMX), both likely chosen as nice multiples of 'round' clocks like 1MHz etc.

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