AUTOHELM Masterview ST80, Manual

Page: 14 / 22

7.3 Signal Processing
Microprocessor
IC13 has a clock rate of 16MHz, determined by crystal XL1.
External and internal inputs, SeaTalk data and signals from the Autohelm
ASIC are processed and the appropriate commands and responses are
generated by the microprocessor.
Outputs from the microprocessor to ASIC IC4 are:
1. Data for the SeaTalk bus (DATA Tx)
2. SeaTalk Enable/Disable (ST_EN)
3. Beeper enable
Other output signals include:
1. Scan signals to keypad switches SW1 - 4
2. Keypad LEDs 1 - 8 illumination through drive transistors TR5, TR6
3. LCD Contrast control is achieved by signals applied to negative voltage
generator IC16 via a current amplifier/integrator formed by transistors
TR3, 12 and capacitor C8. IC16 generates VEE which is supplied to the
row and column LCD drivers. Contrast control signals V1 - V6 are
produced by a resistor network (R17 - 21) and the four elements of
current amplifier IC10. The signals are applied to LCD row driver IC9
and column drivers IC5, 6, 7, 8
4. Control (D_RES, D/L, R/W) and column/row address (L0 - L7) signals
are supplied to LCD decoder/drivers IC5, 6, 7, 8, 9. Row driver IC9
also generates control signals which are applied internally and to the
column drivers
5. Electroluminescent panel brightness signals are applied through the RC
filter formed by R64 and C45 to the driver circuit based on transistors
TR7, 20, 21 22 and 23
Data Storage
Programs and ‘fixed’ data (including factory - set default values) are held in
FLASH MEMORY IC2.
Other data storage is provided by RAM IC15 which is supplied with a
maintaining voltage from battery B1 in the event of power loss either by
failure or intentional switch - off of the system.
In normal operation, both RAM and FLASH MEMORY are supplied with VCC
through transistors TR18 (FLASH MEMORY) and TR11 (RAM). If the supply
fails, the ASIC, IC4, issues a reset signal which cuts off TR18 via TR17.
Z211Z211Z211Z211Z211
ST80 Masterview
14 Masterview Service Manual 83028_1