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In the early 1980s, a company called Hayes began manufacturing the Hayes Smartmodem 1200. Shortly after that, Hayes was forced to quickly release the Smartmodem 2400, as the market for 1200 baud/bps modems evaporated almost overnight. In the rush to get the Smartmodem 2400 completed and onto the market, there was no time for design alterations or embelishments between these two modem designs. This inadvertantly created a new era in modem standardization that continues today.
The fact of the matter is that the claim that these two modems were "smart" was somewhat feeble, even compared to modems of that day. The Smartmodem 1200 and Smartmodem 2400 could dial telephone numbers by themselves, rather than the typical situation of expecting a human to dial the number on an attached telephone, and when the human heard the remote modem answer carrier, the human would press a "start" button on the modem and hang-up the extension telephone, allowing the two modems to establish a connection. The manual dialing process was fairly common in modems that had been manufactured for use with POTS/PSTN (Plain Old Telephone Service/Public Switched Telephone Network) lines up to the early 1980s. Automatic dialing modems were fairly rare, or the ability for a modem to dial telephone numbers was an extra-cost option. As an example, in 1983 the Radio Shack 1200baud/bps DC-1200 (a relabeled Ventel modem) cost $699 and the auto-dial module cost an additional $150, which could only do pulse dialing. Even the ability to disconnect the data connection frequently required the human to turn the modem off or place it in an on-hook state.
The Hayes Smartmodems also came with speaker, but then you really need the modem to have a speaker if you are going to let it dial numbers, so this probably really should not count as a feature. The Smartmodem 1200 and Smartmodem 2400 didn't know how to recognize a busy signal or the detect the presence of dial-tone, nor any of the dozens of other features now taken for granted in modems produced since the late 1980s.
Now, the Hayes Smartmodems did have support for several specialized applications, like the ability to transmit morse code, work with RTTY and work with amateur radio repeaters, but for people who just wanted to make a data connection, these extras weren't interesting, and most of these special (or hobbyist) features disappeared in later years and hardly any modem maker copied these capabilities.
What did make the Smartmodem 1200 and Smartmodem 2400 unique at that time was that they were the first case of a vendor producing two different speed models of POTS/PSTN modems that accepted the same programming commands. As mentioned above, this was more of an accident than intentional, with Hayes doing a rushed (and minimal) rework of the Smartmodem 1200 design to support the 2400bps speed that the consumer modem market suddenly demanded. However, this did mean that any software that knew how to get a modem to dial a telephone number that worked on the Smartmodem 1200 would also work on the Smartmodem 2400.
At this point in time, there were relatively few commercial dial-up computer services, with Compuserve being the largest by far. Each time a vendor brought out a new modem, it was routine to wait some months for an updated driver to be written to allow a given brand of computer to be able to control the new type of modem and allow that computer and modem to connect to Compuserve. Of course, by the time the Smartmodem 2400 came on the market, there was already a working driver for the Smartmodem 1200 for many computer platforms, so people who bought the Smartmodem 2400 didn't have to wait for the driver to be written; they could use the one written for the Smartmodem 1200. Supporting the Smartmodem 2400 required little more than placing an addendum in the documentation stating that the Smartmodem 2400 would work using the Smartmodem 1200 driver.
Quite a few modem makers suddenly realized the advantage of making newer models of modems have the same command set as previous models, something that few vendors had ever bothered with, and even individual modem designers would routinely develop a completely different command set for each successive modem model that they created. The Smartmodem 1200 and 2400 largely ended that practice throughout the industry, and within six months, several vendors were offering "Hayes compatibile" command sets as an option or the only choice on their modems.
Hayes promptly sued these companies for using the word "Hayes" in their product literature and packaging, so collectively, the other makers started calling their modems "AT Command Set compatible" and continued to mimic the Hayes command set. By 1986, essentially no consumer modems were made that didn't at least have an AT command set emulation mode.
Years later, the TIA/EIA introduced a formal standard with the title "Data Transmission Systems and Equipment - Serial Asynchronous Automatic Dialing and Control", otherwise known as TIA/EIA-602. TIA/EIA-602 is almost identical to the data-specific commands found in the Smartmodems 1200 and Smartmodem 2400. Of course, by the time the TIA/EIA-602 standard came out, vendors were selling modems with error-correction, compression and far higher speeds. None of these newer capabilities (or the commands needed to control them) are addressed by the TIA/EIA-602 standard, although other standards or drafts of standards exist for commands specific to FAX operations on modems that support FAX transmission or reception, as well as commands specific to voice operations.
For the newer modem-specific features, many manufacturers elected to copy the extensions to the original Hayes command set that appeared in the Hayes Ultra 14,400bps modems. These extensions are largely what Rockwell came up with, who was the primary provider of datapumps to Hayes at that time. Not all modem chipset makers followed the Ultra extended commands to the letter, resulting in some incompatibility that still exists in the more sophisticated commands. These incompatbilities normally surface when the chipset maker isn't Rockwell or a licensee of Rockwells modem code. However, even licensees have altered what Rockwell distributes and in some cases Rockwell has introduced incompatbilities on their own.
Section 2: Summary of the AT Command Set and Syntax (HTML)
Return to The AT Command Set Reference Index (HTML)
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