[continued from previous message]

WW Interface 72000 Atari/Centr, by Wiesemann, Wuppertal
- SIO cable to 36 contact miniature-ribbon plug

Some of the most common Centronics type parallel interface printers used with the Atari included the Star Gemini 10X and SG-10, the C. Itoh ProWriter, and the Epson RX-80, FX-80, and MX-80.

------------------------------

Subject: 5.1) What are the Atari 830, 835, 1030, XM301, and SX212 Modems?

Thanks to Laurent Delsarte for some of the research and writing for this section.

A modem (MOdulator-DEModulator) is a device that modulates an analog carrier signal to encode digital information for transmittal, and also demodulates
such a carrier signal to decode received transmitted information. The common example from the main time period of the 8-bit Atari computers is the voice band modem, otherwise known as a "dial-up modem" that turns the digital data
of a personal computer into modulated electrical signals in the voice
frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data. Thus, in this pre-Internet form of computer networking, any two computers may communicate with each other over a standard telephone line.

The first commercially successful modem was the Bell 103 from AT&T. While the AT&T Bell System maintained monopolistic control over the direct connection to its phone lines in the USA, third-party manufacturers could only offer "acoustic" modem configurations. Acoustic modems featured a cradle designed
to fit snugly around the microphone and earpiece of a standard (of the time) Bell telephone handset. A standard Bell telephone was utilized for its microphone, speaker, and dialing capabilities. Such modems were designed to
be interoperable with the Bell 103, which maintained its role as the effective industry standard.

Later "direct-connect" modems, led by the Hayes Smartmodem, instead connected directly to the phone line. These modems contained their own microphones, speakers, and dialing capabilities controlled via software. The "Hayes
command set" successfully established the industry standard for controlling modem features via computer software.

Most voice band modems have a pass-through line allowing a standard telephone to be physically connected to the line while the modem is also connected. However, voice and data cannot be transmitted at the same time over the same phone line (as is possible with newer telecommunication technologies such as ISDN and DSL). When online using a dial-up modem, before telephone services like voice mail were common, incoming callers would experience a "busy signal" as if someone was already talking on the line. This limitation was finally addressed in 2001 with the V.92 modem standard. V.92 includes a "Modem On Hold" capability, especially useful in combination with the phone company's "call waiting" and "caller ID on call waiting" features.

A wide variety of modulation and communication techniques can be successfully implemented over a standard telephone line. In order for two modems to communicate, they have to initially successfully negotiate the technical
nature of the communications to be used between them. Connection characteristics include modulation technique ("frequency shift keying", "phase shift keying", etc.), operation mode (one-way "half duplex" or bi-directional "full duplex"), synchronization ("asynchronous" data without clock signal or "synchronous" data accompanied by separate clock signal), and bitrate
(measured in bits per second). Early modem users had to become familiar with arcane settings such as these in order to establish successful modem to modem communications. In time, modem modulation standards were established and adopted by the industry, allowing for the details to largely become
transparent to the user. Newer modems would simply negotiate the fastest and most reliable connection possible between them, given the best capabilities of both modems. Major modem modulation standards:

Standard (Year appeared) Top Bitrate Baud(symbols per second)
Bell 103 modem (1962) 300 bit/s 300 (V.21 precursor)
Bell 212A modem (1977) 1200 bit/s 600 (V.22 precursor)
V.22bis (1982) 2400 bit/s 600
V.32 (1986) 9600 bit/s 2400
V.32bis (1991) 14400 bit/s 2400
AT&T V.32ter (1993) 19200 bit/s 3200 ("V.32terbo"; V.34 precursor)
Rockwell V.FC (1993) 28800 bit/s 3200 ("Fast Class"; V.34 precursor)
V.34 (1994) 28800 bit/s 3200
V.34 (1996) 33600 bit/s 3429 ("V.34 Plus" or "V.34bis")
US Robotics X2 (1997) 56000 bit/s 8000 (V.90 precursor)
Rockwell K56flex(1997) 56000 bit/s 8000 (V.90 precursor)
V.90 (1998) 56000 bit/s 8000
V.92 (2001) 56000 bit/s 8000

At the time, it was very common for modem speed bit rates to be incorrectly referred to as "baud" rates. Other than the early 300 bit/s / 300 baud modulation standard this was never correct usage of the term. Baud always meant "symbols per second" rather than "bits per second."

Two additional important modem standards emerged in 1990: V.42 error control and V.42bis data compression. V.42 and V.42bis were implemented in some later V.22bis and V.32 modems, and probably in all modems supporting V.32bis and up. V.92 modems, which appeared in 2001, support V.44 data compression, an improvement over V.42bis compression.

In the early 1980s popular early commercial online services reached via dial- up modem included CompuServe Information Service, Dow Jones Information Service, and The Source. In addition to CompuServe, later online services popular with Atari users included Delphi and GEnie. Modem users would also dial in to mainframe computer systems at universities, or they would log in to privately-operated Bulletin Board Systems running on other personal computers. As long-distance telephone services were billed by the minute, telephone bill expenses were an important consideration.

Atari produced several modems for use with the 8-bit Atari computers. Each Atari brand modem supports U.S. modulation communication standards only; Atari did not market their modems in Europe.

Atari 830 Acoustic Modem
- Also included, boxed, in the Communicator kit CX484
- Type: Acoustic, frequency shift keying (FSK)
- Speed: Up to 300 baud
- Compatibility: Bell 103/113 modem compatible (U.S. industry standard)
- Requires Atari 850 Interface Module or equivalent to connect to the
Atari computer. Connectivity: RS-232-C serial. Pinout:
14 25
o o o o o o o o o o o o DB-25 Socket - female
o o o o o o o o o o o o o
1 13
2. XMT Transmit Data (Input to modem)
3. RCV Receive Data (Output from modem)
5. CTS Clear to Send (Output from modem)
6. DSR Data Set Ready (Output from modem)
7. n/a Signal Ground (Common)
8. CRX Carrier Detect (Output from modem)
- Shipped with an Atari CX87 Modem Cable (830 to 850 serial)
- Made in USA for Atari by Novation, based on the Novation CAT modem
- Top: Ready and Power LED indicator lights
- Side (left-to-right):
- "O / OFF / A" switch: Originate mode / Power Off / Answer mode
- Power input jack
- "F / TST / H" switch: Full duplex mode / Test mode / Half duplex mode
- Serial port
- Transmitter frequencies
- Originate: mark, 1270Hz; space 1070Hz
- Answer: mark, 2225Hz; space 2025Hz
- Receive frequencies
- Originate: mark, 2225Hz; space 2025Hz
- Answer: mark, 1270Hz; space 1070Hz
- Receive sensitivity: -45dBm
- Power: Uses an external power supply that delivers 20V AC @ 400mA, such as
the Atari #CA016751-01 / Novation 901017 or equivalent.
NOTE: Atari product catalogs variously list the minimum power rating for
the 830 at 7 watts or 18 watts)
NOTE: Both the 830 box and the 850 Interface Technical Manual indicate
that the 830 requires:
Input: 117V AC (4 watts)
Output: 24V AC @ 150mA
Is there an Atari-branded supply like this?????
- Manuals:
- Atari 850 Interface Module Operator's Manual C015953 Rev. 1 1980
(preliminary version shipped with earlier/most 850 units; 102 pages)
- See Appendix 13: Atari 830 Modem, pages 97-102
- Atari 850 Interface Module Operator's Manual C017651 REV. B 1982 (15 p.)
- Contains instructions for both the 850 interface and the 830 modem

Atari 835 Direct-Connect Modem
- Sold only as part of the Communicator II kit CX488
- Type: Direct-connect modem
- Speed: up to 300 baud
- Compatibility: Bell 103/113 modem compatible (U.S. industry standard)
- Connectivity: 2 Atari SIO ports for direct connection to Atari computers
- Line jack (RJ11C standard)
- Telephone jack (RJ11C standard)
- Intel 8048 microcontroller, C060549
- The 835 communicates with the computer using the normal SIO protocol at a
rate of 300 baud. (Field Service Manual p.1-2)
- Texas Instruments TMS99532 frequency-shift keying (FSK) modem chip, FC100279 - Made in USA for Atari by Racal-Vadic
- No speaker, but telephone sound can be routed to the computer audio output
- Pulse dialing only
- Power: external power supply that delivers 20V AC @ 330mA, such as the
Atari #C060479 or equivalent
NOTE: Atari product catalogs list the minimum power rating for the 835 at
18 watts, but Atari's own power supply is only rated for 9 watts)
- Technical manual:
- Atari 835 Direct Connect Modem Field Service Manual FD100268

Atari 1030 Direct-Connect Modem
- Speed: up to 300 baud
- Compatibility: Bell 103/113 modem compatible (U.S. industry standard)
- Connectivity: 2 Atari SIO ports for direct connection to Atari computers
- Shipped with SIO cable CA014122 (3-foot)
- Modular Telephone Jack (RJ11C standard)
- Built-in telephone connector cable - for standard RJ11 jack on telephone - The 1030 uses a non-standard protocol for communication commands on the SIO
bus. When a connection is active, the computer and the modem exchange data
directly on the bus at 300 baud, without using [SIO] command or data frames.
(Altirra manual p.162)
- Made in USA; modem electronics by Penril
- Communications are possible with both originate-only and answer-only modems
- Built-in ModemLink telecommunications software
- Bootstrap without disk drive-- With no powered disk drive #1 present,
ModemLink (with integrated T: modem device handler) loads from the ROM of
a powered 1030 into computer RAM on system startup. (The 1030
masquerades as disk drive #1, responding to the Atari OS attempt to boot
from disk.) An extended beep is emitted through the computer's audio
signal as the program is loaded, then ModemLink runs.
- The T: handler can also be loaded from 1030 ROM into computer RAM later;
many alternatives to the 1030 ROM T: handler exist as well. Please see a
separate section of this FAQ list regarding R: and T: modem device
handlers for the 1030 for more details.
- Controls, software selectable:
- Full and Half duplex operation
- Pulse or Tone dialing
- Tones for tone dialing are generated by the computer and reach the
1030 via the SIO sound INPUT line (thanks to audio noise/leakage)
- Tone dialing not available on the 400 (Owner's Guide page 7)
- Memory buffer on/off
- Printer on/off
- Box sticker: "Free Time Offer Enclosed: Dow Jones News/Retrieval Service"
Shipped with CompuServe IntroPak as well
- Receive sensitivity: -43dBm
- Indicators:
- Power ON/OFF
- On-line (carrier detect) LEDs
- Power: external power supply that delivers 9V AC @ 5.4mA, such as Atari
#C062195 or equivalent
- Manual:
The Atari 1030 Modem with ModemLink Telecommunications Program Owner's Guide
C061798 (1983)
- 1030 Designers: John Curran, Ken Fowkes, Sherwin Gooch (project director),
Joe Miller, Songly Mu, Bernie Poggi, Mark Rustad, Phil Schug, Dennis Smith,
Jose Valdes, Vince Wu
- Tone Dialer: * Original version by: J. W. Tittsler, Feb. 1983
* Final version by: M. D. Rustad, May, 1983
* Modified by: J. B. Miller, August, 1983

Atari XM301 Modem
- Type: Direct-connect modem
- Speed: up to 300 baud
- Compatibility: Bell 103/113 modem compatible (U.S. industry standard)
- Incompatibilities: Cannot be used with an Atari 1200XL (see Power, below).
The manual reads "You cannot use the XM301 modem with an Atari 1200XL
computer unless it has been modified. Contact your local Atari service
center for information on modifying your 1200XL computer."
- Additional hardware requirement: (none)
- Connectivity: Built-in SIO cable - must end SIO daisy chain
- Modular Telephone Jack (RJ11C standard)
- Software-compatible with the Atari 1030.
- Key engineer/designer: Jose Valdes at Atari
- Made in Taiwan
- No speaker, but telephone sound can be routed to the computer audio output
- Auto-dial and auto-answer capabilities
- Dialing capabilities: Tone and pulse (rotary) dialing
- Shipped with XE Term Communications Program disk (DX5076)
- Developed by Russ Wetmore for Atari
- Box sticker: "Free Inside/Special Offer: Money Saving Values from the
Source, CompuServe, Dow Jones News/Retrieval Service, Knowledge-Index, and
the Official Airline Guide."
- Transmitter frequency
- Originate: Mark 1270Hz +/- 0.5%; Space 1070Hz +/- 0.5%
- Answer: Mark 2225Hz +/- 0.5%; Space 2025Hz +/- 0.5%
- Transmit level: -9.0dBm to -16dBm
- Receiver frequency
- Originate: Mark 2225Hz +/- 30Hz; Space 2025Hz +/- 30Hz
- Answer: Mark 1270Hz +/- 20Hz; Space 1070Hz +/- 20Hz
- Sensitivity: -13dBm to -46dBm
- Carrier detect threshold
- On: -44dBm
- Off: -45dBm
- Bit error rate: No more than 1 in 10E5 bits
- Power: 5V @ 60mA, drawn from SIO pin 10 (+5V/Ready)
- Manual: Atari XM301 Modem Owner's Manual C026119 (1985)

Atari SX212 Modem
- Type: Direct-connect modem
- Speed: 75-300 and up to 1200 bit/s
- Compatibility: Bell 103/113/212A modem compatible (U.S. industry standards)
- Hayes command set compatible
- Connectivity: - Atari SIO (must be at end of of SIO chain)
- Uses SIO Motor Control; only one such device can be
attached to the system at a time.
- DB-25S RS-232 serial
- Telephone Line Jack (RJ11C standard)
- Key engineer/designer: Jose Valdes at Atari
- Made in Taiwan
- Built-in speaker with adjustable volume for call monitoring
- Auto-dial and auto-answer capabilities
- Operation: Full duplex and half duplex
- Dialing capabilities: Tone and pulse (rotary) dialing
- Carrier frequencies
- 1200 bit/s; Originate; Transmit 1200Hz, Receive 2400Hz
- 1200 bit/s; Answer; Transmit 2400Hz, Receive 1200Hz
- 75-300 baud; Originate; Mark 1270Hz, Space 1070Hz
- 75-300 baud; Answer; Mark 2225Hz, Space 2025Hz
- Receive signal frequency tolerance: +/- 7Hz
- Bit error rate: Less than 1 in 10E5 bits for signal-to-noise ratio of 8dB
with 300Hz to 3400Hz Gaussian noise over a receive level range of -10dBm to
-35dBm
- Loss of carrier: Disconnects automatically in 1 +/- 1 second after loss of
carrier
- Command buffer: 40-character command buffer
- Receiver sensitivity: -40dBm
- Transmit level: -9dBm
- SX Express! sold separately (DX5089)
- Package includes Program Disk, User's Manual, SIO cable CA014122 (3-foot)
- SX Express! Program Disk (DX5089) includes:
DOS.SYS DOS 2.5 File Management Subsystem (FMS)
DUP.SYS DOS 2.5 Disk Utility Package (DUP)
AUTORUN.SYS SX Express! Ver. 3.00 by Keith Ledbetter
RAMDISK.COM Sets up DOS 2.5 RAM drive for 130XE banked memory
HANDLER.OBJ R: device handler (by Paul Swanson)
HANDLER.DOC SX212 Modem Handler Technical Description
- Power: External 500mA 9V DC (center positive). Shipped with Atari C016353.
- Manual: Atari SX212 Modem Owner's manual C070878 C033506 (1987)

------------------------------

Subject: 5.2) What other modems can I use with my Atari?

Some third-party modems were marketed for use with the Atari 8-bit computers. All of these are direct-connect modems (plug directly into the phone line) unless stated otherwise.

Microconnection A1, by The Microperipheral Corp. (1981)

- 300 bit/s, Bell 103 compatible
- (No Auto-Dial, no Auto-Answer)
- Requires 850 interface, Atari cable included (Atari CX87 equivalent)
- Software included: Tariterm (both cassette and disk, version 1.1, 9/15/81)
- Sold separately: TSMART (cassette)

Microconnection A1A, by The Microperipheral Corp. (1981)

- 300 bit/s, Bell 103 compatible
- Auto-Dial (pulse dialing, not touch tone) / Auto-Answer
- Requires 850 interface, Atari cable included (Atari CX87 equivalent)
- Software included: Tariterm (both cassette and disk, version 1.1, 9/15/81)
- Sold separately: TSMART (cassette)

Microconnection A2, by The Microperipheral Corp. (1981)

- 300 bit/s, Bell 103 compatible
- (No Auto-Dial, no Auto-Answer)
- RS-232 serial printer port included
- Connects via SIO, must be at end of SIO chain. Not a smart SIO device.
- No software included(?). Sold separately:
- Typer-A (M: serial printer device handler on cassette)
- TSMART (cassette)

Microconnection A2A, by The Microperipheral Corp. (1981)

- 300 bit/s, Bell 103 compatible
- Auto-Dial (pulse dialing, not touch tone) / (No Auto-Answer)
- RS-232 serial printer port included
- Connects via SIO, must be at end of SIO chain. Not a smart SIO device.
- No software included(?). Sold separately:
- Typer-A (M: serial printer device handler on cassette)
- TSMART (cassette)

AutoPrint Microconnection, by The Microperipheral Corp. (1983)

- For Atari or Commodore computers
- 300 bit/s, Bell 103 compatible
- Auto-dial / auto-answer
- Printer port - "Centronics" parallel output interface
- Hardware ability to route incoming modem text directly to printer port
- Connects via SIO, must be at end of SIO chain.
- Terminal software listings provided in the user manual. Sold separately:
- TSMART (cassette)

RS-Coupler 9201, by International Quartz Limited (Interquartz) (1983?)

- Acoustic Modem
- 300 bit/s, CCITT V.21
- Originate / Answer
- Requires 850 interface
- Software listings for: IBM PC, Apple II, Atari 800, TI 99/4A, Commodore 64
- http://preview.tinyurl.com/pgdcgdn

Signalman Mark II Atari, by Anchor Automation (1983)

- Model 300-232 09M
- 300 bit/s, Bell 103 compatible
- Auto-dial (no auto-answer?)
- Requires 850 interface, Atari cable built-in (Atari CX87 equivalent)

Volksmodem VM1, by Anchor Automation (1983)

- 300 bit/s, Bell 103 compatible
- (no auto-dial, no auto-answer)
- Voice/data switch, full duplex/half-duplex switch
- Draws its power from the telephone line, with nine-volt battery backup
- Sold separately:
- C Cable, requires 850 interface (Atari CX87 equivalent)
- F Cable (1984), connects to Atari joystick port #2
- Shipped with cassette based terminal software (what software????)
- Uses MPP-1000C/MPP-1000E/300AT modem driver software

Pocket Modem, by BOT Engineering

- 300 baud
- Auto-answer
- Connects directly to SIO
- Uses SIO Motor Control; only one such device can be attached to the
system at a time.
- Pocket Modem cartridge, "Intelligent Terminal Software (c) 1984" contains:
- Pocket Modem Software Ver 2.08 By ADCM Systems (C) Copyright 1984

MPP-1000, by Microbits Peripheral Products (1982)

- Same as: Anchor Automation Signalman 300-232 09F
- 300 bit/s, Bell 103 compatible
- (no Auto answer / no Auto dial)
- Connects to joystick port #4 (400/800 only)
- Smart Terminal tape/disk both included

MPP-1000C, by Microbits Peripheral Products (1983)

- Same as: Anchor Automation Signalman Auto300-232
- 300 bit/s, Bell 103 compatible
- Auto answer / Auto dial
- Connects to joystick port
- Smart Terminal cartridge
- CompuServe DemoPak

MPP-1000E, by Microbits Peripheral Products (MPP) (1985)

- Later units sold/supported by Supra
- 300 bit/s, Bell 103 compatible
- Auto answer / Auto dial
- Connects to joystick port
- Smart Terminal cartridge
- CompuServe DemoPak

300AT, by Supra (1986)

- Supra-branded replacement for the identical MPP 1000E
- 300 bit/s, Bell 103 compatible
- Auto answer / Auto dial
- Connects to joystick port
- Smart Terminal disk
- CompuServe DemoPak and Delphi membership

1200AT, by Supra (1987)

- Same as: E+E DataComm Avatex 1200
- Low Speed Mode: 0-300 bit/s, binary, serial, asynchronous,
Bell 103 compatible
- High Speed Mode: 1200 bit/s character-asynchronous, Bell 212A compatible
- Command Set: 8 Hayes "AT" commands (other options fixed or not needed)
- Auto-answer / Auto dial (tone or pulse)
- (No speaker)
- Connects to SIO
- Smart Terminal disk
- CompuServe DemoPak and Delphi membership

SupraModem 2400AT, by Supra (1988)

- Asynchronous operation at 300, 1200, or 2400 bit/s
- Compatibilities: Bell 103, Bell 212A, V.22, V.22bis
- Hayes "AT" command compatible (100%)
- Auto-answer
- Auto dial (tone or pulse)
- Speaker built-in
- Connects to SIO via included SupraVerter interface
- Smart Terminal disk

Beyond the above modem models, most any industry standard (of the time) external RS-232-C serial modem can work well with the Atari. These were commonly sold for PCs for many years. The Hayes Smartmodem more or less defined the market for these, initially. Normally modems featured a DB-25S connector for interfacing to the computer.

The original, most common, and most trouble-free way to use such a modem with the Atari is to attach it to the #1 RS-232-C serial port (DE-9S) of the Atari 850 Interface Module or equivalent, using an Atari CX87 Modem Cable or equivalent (DE-9P to DB-25P). Note that the standard "modem cable" used with PCs of the era was DE-9S to DB-25P. Such a cable combined with a simple DE-9 P-P gender converter creates the equivalent of the Atari CX87 Modem Cable.

A less common way to connect a standard external modem with DB-25S connector
to the Atari is to connect it to the Atari SIO port via an R-Verter Serial Bus Modem Adapter (Atari SIO to DB-25P) by Advanced Interface Devices (A.I.D.), later sold as the SupraVerter by Supra, or equivalent.
- The R-Verter uses SIO Motor Control; only one such device can be attached
to the system at a time.

The Datatari serial interface cable by Miracle Technology (UK) Limited, later produced by Gralin International, is very similar to the R-Verter/SupraVerter.
- The Datatari uses SIO Motor Control; only one such device can be attached
to the system at a time. (inferred from Multi-Viewterm User Guide p7)

Note that the top modem bitrate that can be utilized by the Atari, under ideal circumstances, is 19200 bit/s. Modems capable of faster bitrates work fine, they just can't be operated at their full speeds.

Later external modems designed for newer PCs connected to a USB port on the PC instead of the standard DE-9P serial port found on earlier PCs.

------------------------------

Subject: 5.3) What should I know about using fast modems with the Atari?

While Atari never marketed a modem faster than the 1200 bit/s SX212, the Atari is capable of supporting modem bitrates of up to 19200 bit/s, depending upon circumstances described here.

Several factors come into play in using modems faster than 2400 bit/s with the Atari.

Firstly, the top bitrate supported by a given software application on the
Atari can be the determinative limiting factor. Many programs on the Atari
may not support, or may not be able to keep up with, bitrates greater than
1200 bit/s or 2400 bit/s.

Assuming the use of an Atari program that supports higher speeds, it will be useful to have an understanding of data flow control. Here is a definition of flow control from: http://preview.tinyurl.com/p8muzmp

Often, one modem in a connection is capable of sending data much faster than
the other can receive. Flow control allows the receiving modem to tell the
other to pause while it catches up. Flow control exists as either software
(XON/XOFF) flow control, or hardware (RTS/CTS) flow control. With software
flow control, when a modem needs to tell the other to pause, it sends a
certain character, usually Control-S. When it is ready to resume, it sends a
different character, such as Control-Q. Software flow control's only
advantage is that it can use a serial cable with only three wires. Since
software flow control regulates transmissions by sending certain characters,
line noise could generate the character commanding a pause, thus hanging the
transfer until the proper character (such as Control-Q) is sent. Also,
binary files must never be sent using software flow control, as binary files
can contain the control characters. Hardware, or RTS/CTS, flow control uses
wires in the modem cable or, in the case of internal modems, hardware in the
modem. This is faster and much more reliable than software flow control.

Some/later 2400 bit/s modems, and probably all modems with 9600 bit/s speed capabilities and up, normally use V.42 standard error correction and V.42bis standard data compression. Subjectively, V.42/V.42bis are nice at 2400 bit/s, important at 9600 bit/s, and essential at any speeds beyond 9600 bit/s.

V.42bis requires hardware flow control (and V.42 error correction). But with Atari equipment (except the MIO and Black Box) hardware flow control is not supported so V.42bis cannot be used and should be disabled. Standard Hayes modem command to disable V.42bis data compression: AT&C0

While V.42 error correction can technically work with either software or hardware flow control, for reasons described above it is typically only used when hardware flow control is available. Since Atari equipment (except the
MIO and Black Box) does not support hardware flow control, V.42 should generally be disabled. Standard Hayes modem command to disable V.42 error correction: AT&K0
Note that disabling V.42 also has the effect of disabling V.42bis.

Finally, hardware ports on the Atari have their inherent top bitrate limits. The serial ports of the Atari 850, for example, support a top bitrate of 9600 bit/s. Other modem interfaces for the Atari may support bitrates of up to 19200 bit/s.

Clay Halliwell offers a tip on achieving 9600 bit/s through the 850 Interface:
On 11 Feb 1996, Marc G. Frank said:

> I'm having problems getting a modem attached to my Atari 850 to
> communicate at 9600 baud. When I set my communications program to 2400
> baud, everything works fine. However, when I set it to 9600 baud, the
> modem echoes my characters but doesn't act on them.

The problem with the 850 is that some of them (like mine) don't produce a
PERFECT 9600 baud signal. As a result modems can't train on it, and while
they will echo characters back, for some nitpicky reason they won't pick up
on the "AT" attention code.

The solution is to do all your dialing at 2400 baud, but set the S37
register to force the modem to try to connect at 9600. Then switch your
Atari to 9600 after connecting.

------------------------------

Subject: 5.4) How do I transfer files using a null modem cable?

A null modem cable can be used to transfer files between two computers that
are physically near enough to each other to be connected by a cable. The
cable has an RS-232 serial connector at both ends, for connecting to RS-232 serial ports on both computers.

Minimally, the null modem cable contains just three connections: transmit data (TD or XMT), receive data (RD or RCV), and ground (GND), with the transmit and receive data pins crossed between the two ends of the cable. A null modem
with these three lines is suitable for connections of up to 4800 bps. For faster connections, requiring hardware flow control, more pins must be connected, and additional lines crossed, between ends of the cable.

Null modem wiring diagrams for standard DB-25 and DE-9 RS-232 serial ports are available at https://en.wikipedia.org/wiki/Null_modem. The pinouts for the RS-232 serial ports of the Atari 850 Interface are provided elsewhere in this FAQ list.

The Atari CX88 Terminal Cable (DE-9P to DB-25P) is a null modem cable suitable for use with the 850 interface, assuming a DB-25S RS-232 port on the other computer. Note that the standard RS-232 serial port on a PC is not DB-25S,
but either DE-9P or DB-25P. So, a standard gender changer, and possibly a standard DE-9 to DB-25 adapter, may also be needed if using the Atari CX88 Terminal Cable as a null modem cable.

Terminal telecommunications software, designed to connect to a remote computer through an RS-232 serial modem connected to a standard phone line, and which supports standard file transfer protocols such as XMODEM, YMODEM, or ZMODEM,
is run on both computers. Programs supporting XMODEM, YMODEM, or ZMODEM that are listed in section 8.15 of this FAQ list, "What noncommercial telecommunications programs are there?", are suitable for this purpose on the Atari.

------------------------------

Subject: 5.5) What networking hardware is there for the Atari?

Supra MicroNet (developed by MPP, released by Supra) (1985)

Share one SIO chain of peripherals (printers, disk drives, modems) among up to 8 computers. When one computer accesses a peripheral device, the entire bus
is occupied so that the other computers on the "network" must wait. The bus
is freed five seconds after a computer finishes interacting with the peripheral. Shipped with modified Atari DOS 2.5 to support busy disk retry. For sharing a printer, a printer buffer such as the MPP/Supra MicroStuffer for each computer is recommended. Reviewed: http://www.atarimagazines.com/v4n10/productreviews.html

CSS Deluxe Quintopus (1989)

Can be used to "share" up to 4 SIO device chains between two computers. Unit includes 2 switched SIO ports and 4 unswitched SIO ports. Two computers can
be connected to the two switched ports, but in this scenario only one of the switched ports can be switched on at a time. http://www.nleaudio.com/css/products/quintopus.htm
(The standard Quintopus is identical except with only unswitched ports.)

CSS Multiplexer ("MUX") (1989?)

Description from the CSS online catalog:
The Multiplexer is a collection of cartridge interface boards that allow up to 8 Ataris to read and write to the same drives (typically a hard disk), access the same printer(s), and talk to each other. It is the first practical networking system for the Atari 8-bit computer.
One "master" computer (any 8-bit) is equipped with the master Multiplexer interface. Then up to 8 "slave" computers hook up to this master, each having their own slave interface. The slave interface consists of a cartridge that plugs into the cartridge port. It has its own socket on the top so you can
use whatever cartridges you desire with the system.
The "common" peripherals (things that are to be shared) are connected to the master. On each slave, all disk and printer I/O is routed through the master so no extra disk drives are needed. The master computer can be configured in any manner you wish. You may have certain peripherals local to the slave or routed to a different number on the master. Note that serial ports (R: RS-232 interfaces) are not multiplexed. All slaves are independent and do not need
to have the same program running on them. http://www.nleaudio.com/css/products/multiplexer.htm

GameLink and GameLink-II

Two hardware designs by Chuck Steinman of DataQue support the linking of two
or more Atari computers. Each supports multiple user head-to-head gaming

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