14.4 Fax Modems
9 messages in this thread
I need some help in using 14.4k fax/modems with my Amiga. The UART chip is 8520
which means that is quite slow. Will I be able to use full speed of the modem
with hardware compression (up to 57,600 bps) using standard Amiga external
port? Thanks for your help in advance,
Janusz,
How fast of a processor do you have?
I use my 1200 at 57600 baud all the time, but I had to install another
serial.device driver called artser.device.
Bob Comer — Cruising the nets on Autopilot!
Cheyenne, Wyoming U.S.A.
I have 68030 25MHz. Does it make a difference? You use 1200, maybe it uses
faster UART chip. Thank for input,
Janusz,
Actually, it does make a difference…
Before I got my accellerator, I was able to communicate at 57600, without
have to use that serial.device that I told you about. (There's some
timing differences when running a faster processor.
I don't think there's any difference in the speed of my "UART", (See
Ronald's explanation of the Amiga's UART chip…) but there's definitely
difference in the speed of the rest of the bus between the 1200 and other
Amiga's.
Which Amiga do you have?
Bob Comer — Cruising the nets on Autopilot!
Cheyenne, Wyoming U.S.A.
I have A2000 with GVP '30 25Mhz. I'm quite sure that it will handle 14.4 modems
well. I didn't realize the difference between IBM UART and Amiga chips. Thank
for your help!
Janusz,
JT >>The UART chip is 8520 which means that is quite slow. Will I be able
to use full speed of the modem with hardware compression (up to 57,600
bps) using standard Amiga external port?<<
A standard Amiga does not have the IBM/Clone UART chip (#8250), the #8520
chip is a custom chip for handling I/O from the serial, parallel,
keyboard,and other Amiga I/O activities.
The Amiga does have a UART contained with in the PAULA chip. This UART is
programable for any rate from 110 to over 1,000,000 bits per second.
However, the Amiga's UART lacks a FIFO for buffering incoming data. With
the CPU multitasking programs, this can lead to problems, IF the CPU can't
return to the serial.device to fetch the incoming data before it is
overwritten.
The faster the CPU the faster it can get it other tasks done, and return
to the serial.device. Having true FAST RAM (system memory), can aid the
CPU in preventing system slowdowns due to the CPU having to access CHIP
RAM (graphic memory).
If you are having problems with the Amiga keeping up with the modem, try
limiting the term's screen colors to 8 or less, and if your term software
allows — increase it's task priorty so the CPU will devote more time to
the terminal.
Also, if you have an A2000/3000/4000, there Amiga serial cards available
if you need a fast UART+FIFO serial port.
Ron.
– ap'ing with AP. (Eagles may fly, but weasels aren't sucked
into jet engines.)
Well I use modems all the time (I work for Supra Corp) my port on my Amiga 2000
with a Turbo 28 (68000 running at 28 MHz) and have the port set to 57600. On
my 3000T at home I set the port to 115,200 (with our new 28.8 modem) and watch
it fly.. I get about 9000-11000 CPS on a text transfer.
Alex
Ronald, Thanks for detailed info.
Janusz,
Janusz,
With a 14.4 modem the 19200 setting is enough. With a 28.8 modem I have
kicked it up to 38400. The highest transfers I have seen are around 3300
with the 28.8. They say in the specs that these modems are capable of
230,400 bps. In the real world, using pre-compressed files, you are only
going to get 3300 to 3500 cps. Which is mind numbingly fast compared to
2400 baud modems.
Don't let the specs boggle your mind. The biggest factor is how clean
your phone line is.
//
Gary Vander Mei on Auto-Pilot \X/