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From: jeff@gatech.CSNET (Jeff Lee)
Newsgroups: net.micro.cbm
Subject: Re: Problems with 1200 baud Kermit
Message-ID: <442@gatech.CSNET>
Date: Thu, 4-Jul-85 11:30:23 EDT
Article-I.D.: gatech.442
Posted: Thu Jul  4 11:30:23 1985
Date-Received: Fri, 5-Jul-85 06:46:35 EDT
References: <180@cernvax.UUCP> <1000014@acf4.UUCP>
Organization: School of ICS, Georgia Institute of Technology, Atlanta
Lines: 27

> I would suppose that the 64 would have MUCH trouble handling
> 1200 baud.  Remember, that's 1200 bps, or 150 characters per
> second.  Very fast for the 64, considering that a routine
> put in the interupt will only strike 60 times per second.

1200 bps (asynchronous) is not quite 150 chars per second. Depending on the
number of stop bits or the length of the character, the data rate drops
fairly quickly. Asynchronous transmission normally uses 1 start bit
(to let the hardware know that another character is coming) plus the number
of bits in the character followed by 1 or 2 stop bits to finish the character
and get ready for another. This means that a single character could require
from 9 to 11 bits for transfer. The following assume 1200 bps transmission:

	1 start + 7 data + 1 stop = 9  bits = 133.3 chars per second
	1 start + 7 data + 2 stop = 10 bits = 120.0 chars per second
	1 start + 8 data + 1 stop = 10 bits = 120.0 chars per second
	1 start + 8 data + 2 stop = 11 bits = 109.1 chars per second.

These also drop lower if you start sending parity bits. I don't have a
Commodore modem, but I doubt that since it is an 8 bits machine that it
uses anything but 7 or 8 bit transmission and almost anything higher than
110 uses only 1 stop bit. This would put it in the 9-10 bit range per
character. Enjoy.....
-- 
Jeff Lee
CSNet:	Jeff @ GATech		ARPA:	Jeff%GATech.CSNet @ CSNet-Relay.ARPA
uucp:	...!{akgua,allegra,hplabs,ihnp4,linus,seismo,ulysses}!gatech!jeff