Atari SX212
| Atari SX212 | |
|---|---|
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| The SX212 in front of its box, with the power adapter, the owner's manual and the SX Express! package (photograph: Atari Museum) | |
| Manufacturer | Atari Corporation; made in Taiwan[1] |
| Type | Direct-connect modem, 300 and 1200 bit/s |
| Release date | Shown at Fall COMDEX, November 1986; shipped September 1987[2] |
| Price | US$99.95[3][4] |
| Interface | RS-232 (DB-25), Atari SIO, RJ11 telephone line jack[5] |
| Compatible | Atari 8-bit computers (Atari 400, Atari 800, XL and XE), Atari ST, IBM PC and compatibles, other RS-232 computers[5] |
| Dimensions | 25 × 15 × 7.5 cm, without power supply and connectors[5] |
| Power | 9 V DC wall adapter, the same type as the Atari 2600's[5][1] |
The Atari SX212 is a Hayes-compatible direct-connect modem that Atari Corporation sold from 1987. It works at 1200 bit/s (Bell 212A) and at 75-300 bit/s (Bell 103), dials by tone or pulse and answers calls automatically.[5] It has two computer ports: a standard RS-232 port for the Atari ST, IBM PC compatibles and other computers with a serial port, and an Atari SIO port, so that an Atari 8-bit computer can use it without an Atari 850 interface.[5] It was the fastest modem Atari sold.[6]
History
[edit | edit source]At the Summer CES in June 1986 Atari showed a Hayes-compatible 1200 bit/s modem for the ST, PC and XE, due to ship by late summer. It introduced the modem as the SX212 at the Fall COMDEX in Las Vegas in November 1986, and shipped it in September 1987.[2] Z*Magazine reported on 18 September 1987 that the first shipment had reached Atari's Sunnyvale warehouse. The box held the modem, a power supply identical to the 2600's, the manual and offers from the GEnie and BIX online services, and the suggested list price was $99.95.[3] Antic reported in April 1988 that the first shipment had sold out quickly.[7]
The 8-bit software was not ready when the modem shipped. Atari planned a separate package with an SIO cable and SX Express!, a version of Keith Ledbetter's Express terminal program, and in the meantime owners used the R: handler written for the A.I.D. R-Verter adapter.[3][8] The FAQ records that Atari shipped SX Express! (DX5089: program disk, manual and a 3-foot SIO cable, CA014122) in spring 1988.[1][2] The Atari Museum says it never reached Atari's retail channels and that copies found behind Atari's Walsh Avenue warehouse were later sold by B&C ComputerVisions and Best Electronics.[9] The FAQ names Jose Valdes as the key engineer on the modem at Atari.[1]
Specifications
[edit | edit source]| Item | Value |
|---|---|
| Data rates | 75-300 bit/s and 1200 bit/s, full or half duplex |
| Standards | Bell 103 and Bell 212A, originate and answer; Hayes command set |
| Modulation at 1200 bit/s | Four-level DPSK; originate transmits 1200 Hz and receives 2400 Hz, answer the reverse |
| Frequencies at 300 bit/s | Originate: mark 1270 Hz, space 1070 Hz. Answer: mark 2225 Hz, space 2025 Hz |
| Receiver sensitivity | -40 dBm |
| Transmit level | -9 dBm |
| Loss of carrier | Disconnects 1 ± 1 s after the carrier is lost |
| Command buffer | 40 characters |
| Telephone connection | FCC-registered; RJ11W, RJ11C, RJ12C, RJ13W and RJ13C jacks |
| Power supply | U.L.-listed wall transformer, 115 V AC 60 Hz in, 9 V DC out |
| Operating environment | 0 to 45 °C, 5 to 95 % relative humidity |
Hardware
[edit | edit source]The modem is built around a Sierra Semiconductor chip pair, the SC11008 modem interface controller and the SC11004 300/1200 bit/s modem.[1] Bob Woolley, reviewing it for Z*Magazine, described the board as a two-chip modem set, two RS-232 receiver/driver chips, an audio amplifier, an LS-series logic chip and a clock generator, with jumpers inside.[10] The case is the one Atari used for the Atari XEP80; Antic pointed out that this is why the XEP80's case has speaker brackets, a hole for a volume control and recesses for eight status lights.[4]
The SIO port is not a normal SIO peripheral connection. Woolley found the SIO command line (pin 7) unconnected and got no reply to a status command at any SIO address, and concluded that the modem passes RS-232 data over the SIO data lines in the way the R-Verter does. The R-Verter handler drove it.[10] Because the modem has only one SIO connector, it must be the last device on the SIO chain. It also uses the SIO motor control line, so only one such device can be connected at a time.[1][4] Woolley found the motor line taken to ground through a 680 Ω resistor inside the modem. That explains the manual's warning that an Atari 800XL cannot run the modem and a cassette recorder together, and he expected the same restriction on every 8-bit model.[10][5]
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Connectors
[edit | edit source]| Pin | RS-232 port | SIO port |
|---|---|---|
| 1 | Protective ground | Clock input |
| 2 | Transmitted data | Clock output |
| 3 | Received data | Data input |
| 4 | Not connected | Ground |
| 5 | Clear to send | Data output |
| 6 | Not connected | Ground |
| 7 | Signal ground | Command |
| 8 | Carrier detect | Motor control |
| 9 | Not connected | Proceed |
| 10 | Not connected | +5 V/Ready |
| 11 | Not connected | Audio input |
| 12 | Not connected | Not connected |
| 13 | Not connected | Interrupt |
| 14-19 | Not connected | |
| 20 | Data terminal ready | |
| 21 | Not connected | |
| 22 | Ring indicator | |
| 23-25 | Not connected |
The SIO column is Atari's standard SIO pinout as printed in the manual; Woolley's review found that pin 7 is not wired inside the modem.[10] The RS-232 port is wired as a modem (DCE).[1] Use a full RS-232 cable: a three-wire cable does not work with this or any smart modem, because the modem needs the computer's data terminal ready signal on pin 20.[3][5]
Front panel lights
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| Light | Meaning |
|---|---|
| HS (High Speed) | On only when the modem is working at 1200 bit/s |
| AA (Auto-Answer) | On when the modem is set to answer incoming calls |
| CD (Carrier Detect) | On when a connection is made with another modem |
| OH (Off Hook) | On when the modem is using the telephone line |
| RD (Receive Data) | Flashes when received data passes to the computer, and when the modem echoes commands |
| SD (Send Data) | Flashes when the computer sends data or commands |
| TR (Terminal Ready) | On when the computer supplies the data terminal ready signal; the modem will not execute commands or pass data without it |
| MR (Modem Ready) | On whenever the modem is switched on |
With the modem connected and switched on, TR, MR and (at 1200 bit/s) HS should be lit. OH comes on when it dials and CD when the other modem answers.[5] Antic found the lights dim and hard to see unless the reader's eyes are level with the modem.[4]
Power
[edit | edit source]The SX212 takes 9 V DC from a wall adapter. The FAQ gives the requirement as 9 V DC at 0.5 A, centre positive, the same as the Atari 2600 and the XEP80, and lists the Atari adapters C010472, C016353 and C018084 as suitable. Later 220 V European adapters (C018084-117) are labelled "For use with models CX2600 XEP80 or SX212".[1][11] Atari's manual says to use only the adapter supplied, because the wrong one can cause irreversible damage to the modem.[5] Check the adapter's output with a meter before connecting an unknown adapter.
Using the modem
[edit | edit source]On an Atari 8-bit computer the modem connects either through an 850 interface or P:R: Connection with a standard modem cable, in which case it behaves as an ordinary Hayes modem, or straight to the SIO chain with an SIO cable. Through the SIO port it needs an R: handler written for it. Programs that carry their own 850 handler, such as 850 Express! and HomeTerm, do not work with an SIO-connected SX212 until patched.[4][8] Handlers that work include the one supplied with SX Express! (by Paul Swanson), the R-Verter handlers, Trent Dudley's SX212 handler, James Dillow's SX212 ATH handler and Bob Puff's BOB-Verter, which supports both the SX212 and the R-Verter.[12]
On an Atari ST the SX212 plugs into the modem port with a standard modem cable and works with any terminal program that drives a Hayes modem.[4] Atari's manual points out that the VT52 emulator on the GEM desktop can dial and go online but cannot send or receive files.[5]
Commands follow the Hayes AT set: ATDT or ATDP to dial by tone or pulse, ATA to answer, ATH to hang up, +++ to return to command mode while online, ATO to go back online and ATZ to restore the default settings. The modem supports 19 S registers, five of them bit-mapped. The I option reports a three-digit product code with the revision number, or a checksum of the modem's ROM.[5] The speaker volume is a recessed screw on the bottom of the case, turned clockwise for louder; Antic needed a long, thin screwdriver to reach it.[5][4]
Troubleshooting
[edit | edit source]| Symptom | Cause and action |
|---|---|
| MR light does not come on | Check that the adapter is plugged in and its round plug is fully seated in the modem, and that the outlet works. If the outlet works and the modem does not, the modem or its adapter needs service.[5] Measure the adapter: it should give 9 V DC, centre positive.[1] |
| Modem does not start properly after being switched off and on | Wait at least two seconds after switching off before switching on again.[5] |
| Modem replies OK but will not carry out commands, TR light off | The computer is not sending data terminal ready. Set it in the terminal program, or use a cable that carries pin 20.[5] A three-wire cable will not work.[3] |
| SD and RD lights do not flash, no data exchanged | Check the cable is in the correct serial port (not a parallel port) and that the software is set to that port. Compare the cable's wiring with the pinout above. Set speed, parity, data bits and stop bits to match the remote system.[5] |
| Tones audible but no carrier detected | Check the telephone connections, especially a Y adapter shared with a telephone; both cords need RJ11C-compatible plugs.[5] |
| 8-bit computer cannot see the modem on the SIO chain | The program has no SX212 handler. Load a handler that supports the SX212, or connect through an 850 or P:R: Connection.[4][12] Make sure the modem is the last device on the chain.[1] |
| Cassette recorder stops working with the modem attached | The modem holds the SIO motor line through 680 Ω to ground. Unplug one or the other.[10][5] |
| Lights hard to read | Normal. They are dim and only visible from straight on.[4] |
Opening the case
[edit | edit source]Atari's manual says the modem has no user-repairable parts and that taking it apart voids the warranty and the FCC registration.[5] The case comes apart as follows, from Tattler Solutions' installation instructions for its replacement board:[13]
- Remove the four screws on the bottom and turn the modem the right way up.
- Lift the top cover at the front, by the lights, to about 20°, which unlatches it from the power connector at the back.
- Push the top cover towards the back until it comes free.
- Unplug the speaker's two-pin connector near the front lights by pulling it straight up.
- Lift out the circuit board, leaving the speaker in the case.
The only Atari document for the SX212 on the Internet Archive is the owner's manual, and bitsavers holds no Atari modem documents. With no schematic or parts list to work from, there is no verified capacitor list for this modem.
Modern replacement board
[edit | edit source]Tattler Solutions makes the SX212 WiFi Retromodem (2026), a board that replaces the original circuit board inside the SX212 case. It is based on the ZiModem 4.0 source code, supports up to 115,200 bit/s on the RS-232 connector and up to 1200 bit/s on the SIO connector, and plays simulated dial tone, dialling, ringing and connect sounds through the original speaker. It runs from its own 5 V 1 A supply; Tattler warns that the original Atari adapter either will not fit or could damage it.[13][1]
Documentation
[edit | edit source]- Atari SX212 Documentation: the owner's manual, with its contents.
- Atari SX212 Modem Owner's Manual (C070878-001 Rev. A, 1987)
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 2 August 2026, section 5.1.1, "Atari SX212 Modem": connections, Sierra SC11008/SC11004 chips, engineer, country of manufacture, SX Express! package, power requirement and the Tattler Solutions board. mcurrent.name. Community reference.
- ↑ 2.0 2.1 2.2 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, section 11.1, history of the 8-bit platform: entries for June and November 1986, September 1987 and spring 1988. mcurrent.name.
- ↑ 3.0 3.1 3.2 3.3 3.4 Z*Magazine no. 71, 18 September 1987, "Atari News Update: SX212 Release" (from GEnie): first shipment, box contents, cable requirement, planned 8-bit package, list price. textfiles.com.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Charles Jackson, "Atari SX212 and SupraModem 2400", Antic vol. 7 no. 2, June 1988: price, case shared with the XEP80, connecting to 8-bit and ST computers, software, speaker volume control and indicator lights. atarimagazines.com.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 Atari Corporation, Atari SX212 Modem Owner's Manual, C070878-001 Rev. A, 1987: introduction (p. 1); required equipment and connecting the modem (pp. 3-7); speaker volume (p. 7); indicator lights (pp. 8-9); VT52 emulator (pp. 3, 12); modem commands (pp. 14-19, table 1 p. 16); options including I (pp. 21-24); S registers (pp. 24-34); troubleshooting and preventive maintenance (pp. 35-38); connector pin assignments (p. 39); specifications (pp. 43-44). Hosted as File:Atari SX212 Modem Owner's Manual C070878-001.pdf.
- ↑ Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, section 7.6, "What should I know about using fast modems with the Atari?": "Atari never marketed a modem faster than the 1200 bit/s SX212". mcurrent.name.
- ↑ "I/O Board: SX212 Software", Antic vol. 6 no. 12, April 1988, editor's reply. atarimagazines.com.
- ↑ 8.0 8.1 Larry Richards, "Atari October News Roundup" (B.A.S.I.C. and Dateline BBS), Z*Magazine no. 76, 23 October 1987, "New Atari hardware now shipping": one SIO connector, SX Express! to follow, the R-Verter handler working with Amodem and HomeTerm. textfiles.com.
- ↑ Curt Vendel, Atari Museum, "Atari SX212 Modem": the modem and the fate of SX Express!. atarimuseum.ctrl-alt-rees.com.
- ↑ 10.0 10.1 10.2 10.3 10.4 Bob Woolley, "Hardware Review: SX212 Modem", Z*Magazine no. 75, 16 October 1987: components inside, SIO command line not connected, R-Verter handler, motor line grounded through 680 Ω. textfiles.com. Reviewer's inspection of his own unit.
- ↑ Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, section 6.2, original equipment power supplies: units C010472 and C018084, their ratings, polarity and labels. mcurrent.name.
- ↑ 12.0 12.1 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, section 7.5, "What should I know about R: and T: modem device handlers?": the SX212 and R-Verter handler lists. mcurrent.name.
- ↑ 13.0 13.1 Tattler Solutions, "Atari SX212 WiFi Retromodem": description and installation instructions. tattlersolutions.com. Retrieved 6 October 2026.