Digital Circuitry - Spacelabs 90217 Service Manual

Ambulatory Blood Pressure Monitor 90217 Service Manual

Digital Circuitry

Display Board
Information is sent from the processor to the LCD controller via a serial bus (CBUS). The LCD
controller activates the necessary segments to display information on the 4-segment LCD. Each of
the segments can be controlled separately. The processor determines which segments must be
turned ON and sends this information to the controller.
An exclusive OR gate blinks the colons once per second when in the clock mode and also
changes drive polarity.
Real-Time Clock
The real-time clock sends and receives data via a bidirectional serial bus that goes to the
processor. The clock is backed up by the 3-volt lithium cell when the main batteries are removed.
The clock uses an adjustable 32 KHz crystal.
RAM
A 128 KB x 8 RAM stores patient collected information, programmed information, and RAM code
software execution. RAM is backed up by the 3-volt lithium cell during main battery removal.
Addressing and Control
Addressing and control are accomplished using a combination of processor ports, latches, and
gates.
Communications RS-232 Connector
The communications connector is a modified RS-232 interface. When the communications cable
(IR cable) is connected to the back of the unit, a reed relay activates the monitor if the power
switch is turned ON.
At this point, the processor checks and determines that the C_CON cable connected line is
asserted and goes into the communication mode. The processor determines whether the cable is
communicating with a modem or a report generator and responds accordingly.
Communications are done using two lines: transmit and receive. Data is converted into IR signals
in the cable and ABP monitor.
Processor
The processor type is an 80C198 with a 7.37 MHz crystal. It contains on-board RAM, ROM, A/D
converter, data ports, addressing control, serial bus lines, and modulator ports that control motor
speed and speaker outputs.
The on-board ROM contains routines for communication and start up. The majority of the ABP
monitor's program is loaded into RAM using the infrared RS-232 port.
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