NGT—Technical description (2010)
NGT Transceiver System Technical Service Manual 97
The backlighting of the LCD is achieved by a bank of LEDs mounted at the back of the
display. The intensity of the backlighting is switched from bright to medium to dark (off)
by switching V3, V4, R36, and R37.
RS232 programming port
IC5 is a complete RS232 driver/receiver with in-built negative voltage generator.
Microprocessor IC1 receives data from IC5 and then re-transmits the data onto the
handset bus. Data received from the handset bus is transmitted by IC5.
Handset data bus
The data bus is a push-pull balanced system and is driven from the CAN driver IC8,
which is controlled by the microprocessor. The data bus connects to the junction box.
The data rate is approximately 125 kbps.
Junction box microprocessor and control
Handset data
Data from the handset is fed via the Audio PCB in the junction box to IC15. IC15
changes the push-pull balanced data to single-ended data, which is read by
microprocessor IC1.
Microprocessor
Microprocessor IC1 has a 16-bit data bus that connects to SRAM IC8 and flash memory
IC4, which contains the firmware. The reset device IC2 resets the microprocessor if the
5 V supply drops below approximately 4.7 V.
UART and dual RS232
UART IC10 is connected to microprocessor IC1 via an 8-bit data bus. The output of the
UART is used to control the dual RS232 IC12, the outputs of which go to the serial port
and the GPIO port.
The UART is also used to drive the diagnostic LEDs H1 to H4, and read the links LK1 to
LK4.
Drawing 04-03125
Drawing 04-03125
Drawing 04-03133
Drawing 04-03133
Drawing 04-03133
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