baud rate is usually 150 times an integer power of 2

[tramu]

Dear Sir,
I want to know the reason, in RS232 standard, why buad rate is usually 150 times an integer power of 2. like 150, 300, 600, 1200, 2400, 4800, 9600, 19200.

Why it is fixed ?

Thanks in advance for any words of wisdom.

Regards,
Thulasi

 

[betwixt]

I *THINK* the reason dates back to mechanical teleprinter machines which had a top speed of 50 Bauds and then the first electronic modems which were acoustically coupled (microphone and loudspeaker) to a telephone handset which had a top speed of 300 Bauds. The natural progression of electronic modems was to double their speed at each step. The doubling was for two reasons, firstly it is easy to generate frequencies in multiples of two and secondly, the higher data speeds, at least over copper were achieved by doubling the points in their constellation patterns.

There is actually no need to stick to these speeds. any can be generated and used but obviously it helps if everyone follows the same standards.

Brian.