gilgut@cg-d.UUCP (Steve Gilgut X5277) (01/08/87)
I have a Multitech Multimodem (300/1200) That I would like to connect to my Atari 800XL I hate the thought of buying an Atari modem when I have a modem already. Any help would be appreciated! Also, what does anyone think of a UNIX look-a-like for the XL family? Advance warning: 2 of 4 disk drives are just for swap! Thanks in Advance, Steve Gilgut -- The Opinions stated herein, etc, ad nauseum..... One if by LAND, Two if by UUCP. :-) Steve Gilgut Compugraphic Corp. M/S 200-1-7H decvax\ 200 Ballardvale St. >!cg-d!gilgut Wilmington, Mass. 01887 ima/
ekijak@ARDEC.ARPA.UUCP (02/04/87)
I don't know how to do it, but you ought to be able to use any modem with
your 8 bit machine. I found out by accident that the 8-bit operating system
which is built into the machine (i.e., it's there even if you don't have a disk
drive)includes software for inputting and outputting data on the serial port.
It follows the standard custom of sending the bytes out one bit at a time on a
single pin. Incoming data is received on another pin of the serial port. Each
byte is preceded by a start bit, and is followed by a stop bit, and the data
bits are ordered least-significant-bit first, six more bits, most-significant
bit last. This is standard asynchronous serial transmission with 8 data bits,
one start bit, one stop bit, no parity. The baud rate is settable by pokeing
the appropriate memory locations, and setting up the serial port for
asynchronous I/O is also done by pokeing appropriate codes into the right
addresses. Sorry, I don't have the addresses or the values that must go into
them. These can be found in the hardware manual, or other published literature.You may have to write your own software to configure the port and input and
output the data, unless your already have some program that interfaces with a
modem or does terminal emulation.
On the hardware side, the voltage levels used by the serial port are not
compatible with what a modem expects to see. The serial port operates at TTL
levels: logic 0 = zero volts, logic 1 = 5 volts. The modem expects RS-232
levels: logic 0 = +3 to +24 (I think) volts, logic 1 = -3 to -24 volts. You
must provide the hardware to do the voltage level translation. The easiest way
to do this is to use a chip such as the Maxim MAX232 which requires only 5 volts
and can be powered by the 5 v pin in the serial port itself. This chip
generates its own +9 and -9 volts for the RS232 levels and translates incoming
RS232 levels to TTL levels. Only a few external components need to be connected
to the chip (a few small capacitors and resistors) and the circuit is very
simple (see MAX232 data sheet).
I'm amazed at the number of features that were included in the original
8-bit machines that were not advertised or brought to the attention of
purchasers. Included at no additional expense were horizontal and vertical
smooth and coarse scrolling, animation by page flipping, custom display lists,
sprites, joystick ports that can be used for output as well as input, paddle
ports that can accept photocell and resistance thermometer inputs, tone
generation for dialing touch tone phones, asynchronous serial port for
communicating with modems or other (multivendor) computers. And all this stuff
was accessible through BASIC, worked with only 16kbits of memory, and didn't
require a disk drive or expansion box.ekijak@ARDEC.ARPA.UUCP (10/03/87)
GVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGVGV
From: "Edmund S. Kijak" (IMD-IPAO) <ekijak@ARDEC.ARPA>
To: decvax!cg-d!gilgut@UCBVAX.Berkeley.EDU
cc: info-atari8@SCORE.STANFORD.EDU
Subject: Re: Need modem help
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I don't know how to do it, but you ought to be able to use any
modem with
your 8 bit machine. I found out by accident that the 8-bit operating
system
which is built into the machine (i.e., it's there even if you don't have
a disk
drive)includes software for inputting and outputting data on the serial
port.
It follows the standard custom of sending the bytes out one bit at a
time on a
single pin. Incoming data is received on another pin of the serial
port. Each
byte is preceded by a start bit, and is followed by a stop bit, and the
data
bits are ordered least-significant-bit first, six more bits,
most-significant
bit last. This is standard asynchronous serial transmission with 8 data
bits,
one start bit, one stop bit, no parity. The baud rate is settable by
pokeing
the appropriate memory locations, and setting up the serial port for
asynchronous I/O is also done by pokeing appropriate codes into the
right
addresses. Sorry, I don't have the addresses or the values that must go
into
them. These can be found in the hardware manual, or other published
literature.You may have to write your own software to configure the port
and input and
output the data, unless your already have some program that interfaces
with a
modem or does terminal emulation.
On the hardware side, the voltage levels used by the serial port
are not
compatible with what a modem expects to see. The serial port operates
at TTL
levels: logic 0 = zero volts, logic 1 = 5 volts. The modem expects
RS-232
levels: logic 0 = +3 to +24 (I think) volts, logic 1 = -3 to -24 volts.
You
must provide the hardware to do the voltage level translation. The
easiest way
to do this is to use a chip such as the Maxim MAX232 which requires only
5 volts
and can be powered by the 5 v pin in the serial port itself. This chip
generates its own +9 and -9 volts for the RS232 levels and translates
incoming
RS232 levels to TTL levels. Only a few external components need to be
connected
to the chip (a few small capacitors and resistors) and the circuit is
very
simple (see MAX232 data sheet).
I'm amazed at the number of features that were included in the
original
8-bit machines that were not advertised or brought to the attention of
purchasers. Included at no additional expense were horizontal and
vertical
smooth and coarse scrolling, animation by page flipping, custom display
lists,
sprites, joystick ports that can be used for output as well as input,
paddle
ports that can accept photocell and resistance thermometer inputs, tone
generation for dialing touch tone phones, asynchronous serial port for
communicating with modems or other (multivendor) computers. And all
this stuff
was accessible through BASIC, worked with only 16kbits of memory, and
didn't
require a disk drive or expansion box.