Autohelm Inboard Autopilots (ST6000 and ST7000 systems) Service ...

AutohelmChannel 4 Feedback 1 (FB1)Channel 5 Feedback 2 (FB2)Channel 6 Not usedChannel 7 Not usedIC9 Channel 0 Not usedChannel 1 Not usedChannel 2 Rudder Reference (RUDDER)Channel 3 Supply Monitor (INPUT VOLTS)Channel 4 Not usedChannel 5 Not usedChannel 6 JoystickChannel 7 Not used1.5 Clutch DriveTR10, 11 and 12 switch a nominal 12v onto the actuator clutch whenever pin 15 ofthe microprocessor (IC2) is low at 0v.1.6 Seatalk Bus Transmit and ReceiveSeatalk transmit and receive circuitry consists of TR1,3,4,5,18 and 19 and theirassociated components. Data transmission is at 4800 baud with a low start bit andline idling high. TR1 and Tr2 provide high and low drive respectively, whilst TR3 andR1 give overload protection to Tr2 in the event of misconnection. Tr4 and Tr5 allowthe microprocessor to monitor its own transmissions and also to receive data fromother units on the bus.1.7 Fluxgate driveIC2 produces bursts of 8KHz pulses on pin 2 which are then fed through Tr6,7 and 8and AC coupled to the fluxgate via C3.1.8 E2 promIC8 is an E 2 PROM which allows calibration values to be stored and recalled eachtime after power up. Sequential data is written to the e2 prom on pin 3 and readback on pin 4.1.9 Supply voltage monitorR53 and R54 scale down the supply voltage and feed it through to the A/D converterto enable the microprocessor to transmit a warning on the Seatalk bus if the supplyvoltage drops below 11.2v for 10 seconds or more.SeaTalk Service Manual 3