Kongsberg Simrad IS12, Service Manual

Page: 37 / 67

Issue 1.0 09/06/03
SIMRAD
37
Non-Volatile Memory (NVM) . Integrated Circuit IC1 provides 1Kbit of E
2
memory for the retention
of important data after power down.
CanBus Interface . The IS12 instruments are interfaced by CanBus, a true multi-talker system
with high levels of error protection. The bus protocol is encoded and decoded by the dedicated
CAN Module built into the microprocessor and IC2 acts as the driver providing the physical layer
interface to the interconnection between products. The CanBus data connections are labelled
CANL and CANH.
Crystal Display (LCD) . There are 3 types of LCD dependent upon the display type, Combi and
Data instruments employ a 2 line display (E03680), Depth, Speed and Mega employ a single line
display (E03728) and the Wind instrument employs a small single line display (E03729). All LCD
s are custom made.
The LCD s are driven by Integrated Circuit IC5, a software programmable LCD controller / driver,
under serial control of the microprocessor. The driver operates from its internal clock, the
frequency being set by Resistor R22. Divide by four time division multiplexing acting upon 4
common lines and 32 segments is employed to provide for up to 128 segments. LCD drive levels
are set from the fixed resistor chain R18 to 20 and R110 to R112, the contrast level is therefore
fixed and remains constant across the specified temperature range.
Key Switches . Switches SW1 to SW4 are directly connected to microcontroller ports P1.0 to
P1.3. The lines are normally held high by Resistors R74 to R77 but are pulled to ground when the
switch is operated.
Backlighting . The analogue display backlighting configuration utilises LEDs 1 to 4, 9 and 14 and
15 and the digital display LEDs 5 to 8. Both configurations are driven by the same circuit,
Transistors TR13 and 14, under control of the microprocessor. The circuit provides even
illumination over a variety of supply voltages and the level of illumination is controlled by the pulse
width of the signal applied to the base of TR14 by the microprocessor.
Key Lighting . Key lighting is provided by Transistor TR12 from the same source as the
backlighting. However, the shunt resistor R60 across TR12 provides for continuous low level
illumination when the backlighting is set to off to allow the keypad to be found in very low ambient
light levels.
Audio Sounder . Integrated Circuit IC12 gates IC12a and IC12b are configured as a square wave
oscillator producing a constant output at 2.4KHz. The key beep is generated on any key
depression by the gate applied from the microprocessor port ST3.1 to IC12c. The resulting 2.4KHz
burst is applied to the Piezo Sounder positive connection via FET TR17 to provide sufficient drive.
The extra volume required for the alarm beep is produced by applying the output burst from IC12c
to the input of gate IC12d, enabled by the load alarm signal from the microprocessor port ST3.0.
The resultant anti-phase output from IC12d is applied to the Piezo Sounder negative connection
via FET TR18.