Technical Guidance Notes
Page 28 of 29 ©2007 Siemens Protection Devices Limited
Section 5: Glossary
Baud Rate
Data transmission speed.
Bit
The smallest measure of computer data.
Bits Per Second (bps)
Measurement of data transmission speed.
Data Bits
A number of bits containing the data. Sent after the start bit.
Data Echo
When connecting relays in an optical ring architecture, the data must be passed from one relay to the
next, therefore when connecting in this method all relays must have the Data Echo ON.
Half-Duplex Asynchronous Communications
Communications in two directions, but only one at a time.
Hayes ‘AT’
Modem command set developed by Hayes Microcomputer products, Inc.
Line Idle
Determines when the device is not communicating if the idle state transmits light.
Modem
MOdulator / DEModulator device for connecting computer equipment to a telephone line.
Parity
Method of error checking by counting the value of the bits in a sequence, and adding a parity bit to
make the outcome, for example, even.
Parity Bit
Bit used for implementing parity checking. Sent after the data bits.
RS232C
Serial Communications Standard. Electronic Industries Association Recommended Standard Number
232, Revision C.
RS485
Serial Communications Standard. Electronic Industries Association Recommended Standard Number
485.
Start Bit
Bit (logical 0) sent to signify the start of a byte during data transmission.
Stop Bit
Bit (logical 1) sent to signify the end
USB
Universal Serial Bus standard for the transfer of data.
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