RS-232 and Frequency

[Yin99]

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

 

[Joel Kolstad]

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,

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.

 

[[email protected]]

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

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!

 

[[email protected]]

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

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!

 

[budgie]

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

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

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.

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