Subject: Re: Falcon serial ports
To: None <email@example.com>
From: Howard Chu <firstname.lastname@example.org>
Date: 04/14/1997 14:05:04
Howard Chu wrote:
> Both of the ports are driven by a Zilog 8530 SCC. You can set the clock
> dividers to go up to 230.4kbps if you want. I think that's probably the
> upper limit. I haven't looked at any ISDN modems, do they do speed matching
> for you? (at 2B you're going 128kbps, and most serial ports do 115.2k...)
This might be theoretically sound, but I don't think a Falcon can take serial
I/O at 230.4kbps... I think that 38k4 will be the practical limit. This is
caused by the fact that the 8530 only has a 3 byte fifo. At 230kbps the Falco
has to serve the 8530 at least once per 1/7850 seconds (assuming it reads 3
chars at once, 1 char == 10 bits).
I have heard rumours that the LAN port does not work. I can't try this out
The numbers are accurate enough, but that doesn't preclude operating at
these speeds. Keep in mind that a lousy 128K Macintosh with 7.75 MHz 68000
could handle AppleTalk at this speed - the trick is to only allow interrupts
for the first received byte of a packet, and then run a polling loop until
the end of the packet.
For another data point, I have had no trouble using Zmodem between a TT
and Falcon at 115.2kbps. (This is my fallback when they're too far to do
transfers over SCSI.) When you say "the LAN port does not work," are you
talking basic hardware fault, or software driver problem? I can assure you
that the hardware works as advertised.
Final point - there's nothing preventing you from obtaining an 8530B and
desoldering/replacing your 8530, to get a deeper FIFO, more reliable high
speed operation, etc...