Technical Manual

DISPLAY
M
VIBRATE
MOTOR
LIQUID
EEPROM
CRYSTAL
DISPLAY
MODULE
SRAM
AUDIBLE
ALERT
MICRO-
PROCESSOR
SK1
TAG11122-1
DATA BUS
ADDRESS
CONTROL LINES
DECODER
POCSAG
PL401
PGM
DATA
XL403
SW2
SW3
SW1
!>BUTTON
BUTTON
BUTTON
FROM
RECEIVER
BUS
RESET
IC5
VDD
IC1
IC3
IC402
RESET
DRIVER
DRIVER
TR415
TR3; TR4
TP401
DRIVER
TR2 OR
TR416
SK1 PL401
IC4
RESET
ILLUMI-
NATION
TLA 852/FLA 872
TM1205 Issue 2 Page 3 - 7
Figure 3.3: Decoder Block Diagram
3.3 DECODER
3.3.1 General
The Decoder comprises the POCSAG decoder, Microprocessor, EEPROM, SRAM
message memory and switches, plus support components and a separate LCD
module. The signal from the receiver is processed by IC402, the POCSAG decoder,
and the decoded data passed to the microprocessor. The microprocessor stores the
information in the SRAM, IC4, before activating the selected alert and sending the
message data to the LCD module for display. The EEPROM holds information
applicable to the unit.
3.3.2 POCSAG Decoder
The POCSAG decoder, IC402, is located on the Radio Board of the unit and
connects to the microprocessor, IC3, through PL40I / SK1. Pin 4 of IC402 receives
the data signal from IC401. IC402 decodes the information and sends it, four bytes
at a time, to the microprocessor, IC3. IC402 uses the SCK clock pulses from IC3,
pin 59, to transfer the data on the SDO line, IC402, pin 13.
When no signals are received by the unit, the system goes into a standby mode to
reduce power consumption. In this mode, a pulse from IC402 pin 1 (BS1), sets the
receiver circuits ON for a brief period every 0.5s - 1s, depending upon Baud rate, to
check for a preamble signal. If such a signal is received, followed by a valid address
and message, a signal is sent from IC402, pin 15 (ATTN) to alert the microprocessor.