GE T2100, Service Manual, Page: 62 / 152

5-12 GE T2100 Treadmill Revision A
2021403-031
Theory of Operation: Processor Board (PCB) Theory
Processor Circuitry
The MC9s12DG128 runs at 16 MHz with an internal bus clock of 8 MHz.
Its code is stored in the 128 KB Flash EPROM. The MC9s12DG128
addresses its memory internally. The processor handles all the I/O,
including two serial channels, 4 analog inputs, and digital inputs and
outputs to control the GE T2100 Treadmill grade, speed, calibration and
ESTOP processes.
Analog Inputs
Ratiometric Inputs
Elevation feedback (from the pot), +5.1V ISO ref, VUNREG ref are
designed to take ratiometric voltages referenced to +5.1V ISO as inputs
to the processor.
Temperature Sensor
The processor monitors temperature and saves peak temperature in
EEROM data storage for use by field service. The sensor outputs 10mV/
deg C. The OPAMP provides a gain of 4.92. The MC9s12DG128 ADC will
produce the following output:
!
In hardware
"
ADC value = Temp(deg C) * 10mV/deg C * GAIN * [256(max ADC
counts)/VREF]
!
In firmware
"
Readout temp = (ADC value) * 4 / 10
"
For example:
At 25 degrees Celsius
ADC value = 25 * 0.01 * 4.92 * 256 * /5.1 = 62 (Dec)
Readout temp = 62 * 4 / 10 = 24.8
At 100 degrees Celsius
ADC value = 100 * 0.01 * 4.92 * 256 * /5.1 = 247 (Dec)
Readout temp = 247 * 4 / 10 = 98.8
RS-232/422 Interfaces
The LTC1334 serves as the Host to IFC board transceiver. It translates
the RS422/232 serial protocol voltage levels to TTL levels. The MAX489
is the transceiver for the processor board to drive communication. It
translates RS422 signals to proper TTL levels.