Path: utzoo!utgpu!watmath!att!tut.cis.ohio-state.edu!purdue!iuvax!uxc.cso.uiuc.edu!tank!uwvax!shorty!thaler
From: thaler@shorty.CS.WISC.EDU (Maurice Thaler)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 16450/16550 UART question
Message-ID: <8169@spool.cs.wisc.edu>
Date: 15 Aug 89 21:04:05 GMT
References: <89081106353440@masnet.uucp> <123@fiver.UUCP>
Reply-To: thaler@shorty.cs.wisc.edu (Maurice Thaler)
Organization: U of Wisconsin CS Dept
Lines: 43

In article <123@fiver.UUCP> palowoda@fiver.UUCP (Bob Palowoda) writes:
>In article <89081106353440@masnet.uucp>, william.richardson@canremote.uucp (WILLIAM RICHARDSON) writes:
>> The 16550A is a teriffic UART, It will replace the 16450 or 82450 and
>> give you a 6K buffer that is supported by Telix. It has allowed my USR
>             ^^^ This is a 16 byte FIFO.
>
>> HST 14.4 to work properly @ 38400bps without errors.
>                              ^^^^^^^
>              If this is a V32 modem I doubt that this is the real
>              bps effective out the modem. Most likely it's the 
>              throughput of the modem measured with compression done
>              on the data. Just think if your sending compressed data
>              to the modem already. If you really want to spec a modem
>              modem fairly state:
>              cps/sec uncompressed data
>              cps/sec compressed data.
>              
Actually, most of the high speed modem manufacturers recommend that you
set your high speed modem to lock its speed to the terminal at a rate at
least DOUBLE the actual connect rate. So if you are connected at 9600,
you set your terminal to 19200. If you can achieve higher than 9600 (the
latest HST modems can do something like 14000, than 38400 is the baud
rate you would lock your terminal too. As was stated, with MNP protocol,
you get an increase in speed through data compression, but this does not
happen unless you have both terminals locked to higher rates than the
actual modem rate.

It has been my experience with two HST modems locked to 19200 that I can
get about 1120 bps with ZMODEM. I understand with the new HST's this can
go up to about 1400bps- actual throughput.

It certainly is easy to confuse people with this kind of arrangement.

One important thing to keep in mind if you attempt this higher baud rate
locking is  YOU MUST IMPLEMENT HARDWARE HANDSHAKING!  If you don't, flow
control falls apart completely. On the HST you do this by entering
AT&H1




Maurice Thaler   SYSOP  Audio Projects BBS (608) 836-9473
                 SYSOP  Power Board    BBS (608) 222-8842