Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!phil
From: phil@Apple.COM (Phil Ronzone)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How fast can a MAC-SE drive a serial line?
Keywords: serial, fast
Message-ID: <28564@apple.Apple.COM>
Date: 7 Apr 89 18:05:24 GMT
References: <13655@jumbo.dec.com> <28021@apple.Apple.COM> <1514@ccnysci.UUCP>
Organization: Apple Computer A/UX Group
Lines: 29

In article <1514@ccnysci.UUCP> alexis@ccnysci.UUCP (Alexis Rosen) writes:

Discusssion about LocalTalk and seriol I/O data rates.

>Major nitpick: Both TOPS and Dayna would be surprised to hear that their
>FlashTalk and DaynaTalk products, which run at 768 to 850 kbps, can't
>ever go faster than 500 kbps.

The SCC has a clock MAXIMUM of 4 MHz (unless we have changed to a faster
part lately). The SCC is clocked for baud rate generation at 3.673 MHz.
AppleTalk, which uses SDLC phsyical transmission, runs as FM0 using the
onboard PLL -- thus, at around 4MHZ, 230.4 KB is the fastest you can run
the machine.

In serial I/O, you need to sample at 16X the baud rate. The limiting
factor is the divisor given to divide the clock rate and still sample at 16X.

The SCC is a pretty interesting USUART, but for the current clock rates,
SDLC in FM0 can't go faster than 230.4KB -- serial I think (can't remember)
can be pushed to twice that.
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