Chapter 1: Functional Description; Control Board - GE Giraffe OmniBed Carestation CS1 Service Manual

Chapter 1: Functional Description

This chapter provides a functional description for the device, including sections representing each of the
four boards. Refer to
chapter.

1.1 Control Board

The Intel 80C188EC microcontroller is an enhanced X86 processor with many on-board peripheral features,
such as a interrupt controller, DMA controller, peripheral chip select driver, programmable timers, etc. The
two programmable timers are used to control the two heaters (bed and radiant). The input to these timers is
line frequency. This allows the control signal to be synchronized with the line frequency to better control the
zero-crossing solid state relays. The on-board interrupt controller has several interrupts: analog-to-digital
converter (ADC) conversion ready signal, overtemperature comparator output, watchdog output, power fail
signal, and module interrupt signal from the system data bus. The microcontroller external bus is a
multiplexed address and data bus.
The system memory consists of a programmable read-only memory (PROM) and static random access
memory (SRAM). The EEPROM is used for calibration and biomedical configuration values. This memory
holds the data even after power is turned off.
The RS-485 integrated circuit converts the RS-232 TTL signals from the microcontroller to RS-485 signals for
the bus. This bus is the main communications bus from the control board to the display board, scale, and
servo oxygen board.
There are two isolation transceivers used to isolate the circuits powered by +5V and the circuits powered by
+5VSTBY (PF Battery backup).
The board contains a 16 channel multiplexer. There are seven temperature measurement channels. These
channels measure the two patient skin temperature probes and the compartment probe (with two
thermistors each), and the heat sink sensor used to measure the heat sink temperature. Additional channels
include the humidity sensor (RHIN), LINE COMP & LINE COMP2, 5 Volts, Motor current, Vthref, VDAC, and
1.2Vind.
Attached to the compartment probe connection is the relative humidity signal conditioning circuitry. The 1V
reference that is used for the analog circuitry is also the maximum input voltage and the offset voltage for
the ADC. This yields a purely ratiometric system.
"Figure 1-1 Block Diagram" and section "8.21 Wiring Diagrams" when studying this
1-1