Microprocessors And Control; Handset Microprocessor And Control - Codan NGT 2010 RF Technical & Service Manual

NGT—Technical description (2011/2012)

Microprocessors and control

Handset microprocessor and control

Standby and power on
Drawing
When the transceiver is switched off, the standby indicator LED behind the
illuminated. When the
relay K200 (drawing 04-03369) in the RF unit to be switched on and power is supplied to
the entire system.
Microprocessor
Drawing
The handset has an 8-bit microprocessor IC1. In conjunction with IC3, which contains
the program memory and an I/O expander with internal logic circuits, IC1 controls all the
functions in the handset.
The reset device IC2 resets microprocessor IC1 if the 5 V supply drops below
approximately 4.7 V.
Keypad
Drawing
The row lines (ROW 0 to ROW 2) are held low. When any button on the keypad is
pressed, a low is detected by microprocessor IC1. This causes IC1 to scan the keypad to
identify which button has been pressed, and then perform the function for that button.
The keypad is backlit by LEDs. The brightness of the LEDs is controlled by switching
V1 and V2 as required.
Display
Drawing
The LCD H1 consists of a 98 × 32 dot matrix with LED backlighting. Data from the
microprocessor IC1 is sent via the 8-bit data lines to the display where the in-built
decoder and driver display the information required.
When the user selects to adjust the contrast of the LCD via the appropriate menu in the
handset, the microprocessor IC1 varies the output of the electronic voltage divider IC6.
IC6 feeds the temperature-compensated driver IC7/A. IC7/A has an output of
approximately −1 to −3 V, which is used to set the negative (VEE) level to the LCD to
achieve the required contrast.
124
04-03125
key is pressed, V9 is switched on. This causes the main power
04-03125
04-03125
04-03125
NGT Transceiver System Technical Service Manual
key is