II Glossary
OSW Outbound Signalling Word: data transmitted on the control channel from the
central controller to the subscriber unit.
PC Board Printed Circuit Board
PL Private-Line® tone squelch: a continuous sub-audible tone that is transmitted
along with the carrier.
PLL Phase-Locked Loop: a circuit in which an oscillator is kept in phase with a refer-
ence, usually after passing through a frequency divider.
PTT Push-To-Talk: the switch located on the left side of the radio which, when
pressed, causes the radio to transmit.
RAM Random Access Memory: the radio’s RAM is loaded with a copy of the
EEPROM data.
Registers Short-term data-storage circuits within the microcontroller.
Repeater Remote transmit/receive facility that retransmits received signals to improve
communications coverage.
RESET Reset line: an input to the microcontroller that restarts execution.
RF PA Radio Frequency Power Amplifier
RIB Radio Interface Box
ROM Read Only Memory
RSSI Received Signal-Strength Indicator: a dc voltage proportional to the received
RF signal strength.
RPT/TA Repeater/Talk-Around
Softpot Software Potentiometer: a computer-adjustable electronic attenuator
Software Computer programs, procedures, rules, documentation, and data pertaining to
the operation of a system
SPI (clock and data
lines)
Serial Peripheral Interface: how the microcontroller communicates to modules
and ICs through the CLOCK and DATA lines.
Squelch Muting of audio circuits when received signal levels fall below a pre-determined
value
Standby Mode An operating mode whereby the radio is muted but still continues to receive
data
System Central Con-
troller
Main control unit of the trunked dispatch system; handles ISW and OSW mes-
sages to and from subscriber units (see ISW and OSW).
System Select The act of selecting the desired operating system with the system-select switch
(also, the name given to this switch).
TOT Time-Out Timer: a timer that limits the length of a transmission.
TPL Tone Private-Line
µC Microcontroller
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