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From: markg@amdcad.AMD.COM (Mark Gorlinsky)
Newsgroups: comp.sys.ibm.pc
Subject: Re: PC's serial port
Message-ID: <17080@amdcad.AMD.COM>
Date: Tue, 9-Jun-87 16:09:55 EDT
Article-I.D.: amdcad.17080
Posted: Tue Jun  9 16:09:55 1987
Date-Received: Fri, 12-Jun-87 04:31:09 EDT
References: <2247@husc6.UUCP>
Reply-To: markg@amdcad.UUCP (Mark Gorlinsky)
Organization: Advanced Micro Devices, Inc., Sunnyvale, Ca.
Lines: 21
Keywords: UART serial port baud rate transfer 8250

chamoun@lownlab.harvard.edu (Nassib Chamoun) writes:
>
>On the 8088 PC the 8250 UART (serial port) uses a clock input of 1.8432 MHZ,
>when divided by 16 will yield to the maximum transfer rate of 115,200 bits per
>second.  Can someone tell me if the 8250 on 286 and 386 machines uses higher
>clock rates.

The clock input to the 8250 comes from the crystal oscillator on the interface
card.  Normally this card will work in PCs as well as ATs, so the manufactures
standarize on one design.

Here's a little added info.

The maximum operating frequency of the baud generator is 3.1 MHz.  The fastest 
baud rate at that frequency is going to be 193,750 bps.  

-- 
 Mark Gorlinsky - AMD Processor Products Division/APPS SQA
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