Alan Freedman -- The Computer Language Company - Computer Desktop Encyclopedia
Computer Desktop Encyclopedia
Longest-Running Tech Reference on the Planet

A CDE Definition

You'll love The Computer Desktop Encyclopedia (CDE) for Tech Term of the Day (TTOD)


Hayes Smartmodem

A family of modems developed by Hayes, which was the industry leader for many years (see Hayes). Hayes developed the "intelligent modem" for the first personal computers in 1978, and its command language became the de facto standard for modem control (Hayes Standard AT Command Set).

Two States of Operation
An intelligent modem has a command state and an online state. In the command state, it accepts instructions. In the online state, it dials, answers, transmits and receives.

Once connected, the modem performs the handshaking with the remote modem, which are the whistles and tones you hear from the speaker. This is similar to the opening exchange of a human telephone call: called party says "hello;" calling party says "hello, this is..."; after that, the conversation begins. After the handshake is completed, you are online with the other computer, and data can be transmitted back and forth.

Escape Sequence
The escape sequence tells the modem to switch from online to command state. It consists of three plus signs in sequence (+++) with a Hayes-patented, one-second guard time interval before and after, which prevents the modem from mistaking a random occurrence of plus signs for an escape sequence. The escape sequence and guard time interval can be programmed in the modem's status registers.

To issue an escape sequence, hold down the Shift key and press + three times with a pause of at least one second before and after the sequence. The modem will return the OK result code, indicating it is ready to accept commands.


A company that specialized in modems and remote access products. Based in Atlanta, GA, and founded in 1977 by Dennis Hayes, the company pioneered personal computer communications with the design of its Smartmodem and shipped its first 300 baud model in 1978. Initially Hayes Microcomputer Products, Inc., it became Hayes Corporation in 1997 when it merged with Access Beyond, a spin-off of Penril Data Communications. Hayes filed for Chapter 11 in October 1998 and later ceased operations. Almost all modems use the Hayes command language (see AT command set).

In mid-1999, Zoom Telephonics purchased worldwide product and trademark rights for all Hayes analog modems except the EZ-Jack PCMCIA card. Zoom offers free technical support for the Hayes modems it produces. For more information, visit

ModemExpress, Inc., Monticello, MN, obtained the Hayes domain name ( and provides service and support of Hayes products. See Hayes Smartmodem.

Personal Use Only

Before/After Your Search Term
hashing algorithmHB
Hayes compatibleHD

Terms By Topic
Click any of the following categories for a list of fundamental terms.
Computer Words You Gotta KnowSystem design
Job categoriesUnix/Linux
Interesting stuffPersonal computers
InternetIndustrial Automation/Process Control
Communications & networkingAssociations/Standards organizations
HistoryDesktop publishing
ProgrammingHealthcare IT
System design