RS-232 and Frequency

Jan 05, 2006 4 Replies
Y

If I have to provide a signal through a PC RS-232 port at 15 Hz using



38400 baud, is this possible? What is the max frequency I could support? How would one calculate (derive) these answers?

I know frequency = event / time unit. So 15 Hz is 15 times a second. This seems simple if you are talking about "event" being a simple binary 1 (logic high). That would read "how many times you can pulse a



1 every second". But what if the "event" is a stream of 170 bits? Does that effect the questions above? Note: I am talking about PC PC RS-232 communications (not using a modem). Thanks,

yin99



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J

Come on, surely this is a homework question, right?

First, realize that with RS-232 "baud"="bits per second". So you can send

38,400 bits per second... you want to send an "event" consisting of 170 bits at 15HZ, so that's 170*15=10,650 bits per second -- clearly this will fit through a 38,400 bps 'pipe.'

This does get trivially tricker in that usually one speaks of sending a byte from their PC and this takes more than 8 bits over RS-232 since you have to add at least a start and stop bit (and may add more... parity, longer stop bits, etc.) -- hence requiring at least 10 RS-232 bits to send one byte of data -- but since you question doesn't mention this, I'm assuming it's immaterial.

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S

On a side note, this is one of the reason I like to use the 8N1 for mat so much. It's 10 bits per byte. 38400 baud? Why, that's 3840 kB/s!

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S

On a side note, this is one of the reason I like to use the 8N1 for mat so much. It's 10 bits per byte. 38400 baud? Why, that's 3840 kB/s!

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B

it walks like a duck, it looks like a duck, it sounds like a duck .....

Of course the O/P could simply toggle a handshake line ....

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