Physio Control LIFEPAK 9 - Page 39

Display/Recorder
Interface
© August 1993 Physio—Control
Description 1
microprocessor. An internal oscillator in the System microprocessor
provides four tone frequencies, including the key-click response when a
pushbutton is pressed. Three output lines, VOL1 through VOL3, produce
eight volume levels. The audio is silenced by turning off the System
microprocessor internal oscillator.
Charge Control. The System microprocessor initiates and monitors charge
requests to the D/A converter U18 on the Power Conversion PCB. The I/O
Clock, Converter Function Select, Converter Data In, and Converter Data
Out lines accomplish serial communication with the D/A converter. Pressing
CHARGE on the keypad transmits the coded selected energy value from the
System microprocessor to the Power Conversion PCB over the Converter
Data Out line. Status information on the decoding process on the Power
Conversion PCB is sent back to the System microprocessor over Converter
Data In. The I/O Clock provides synchronous timing for serial
communication.
Following the charge initiation, the System microprocessor performs a set of
self-tests which are completed before the selected energy is available. Ifa
self-test fails, the CRT displays the SERVICE indicator.
The energy stored in the energy storage capacitor is monitored through a
10-bit A/D converter (U9) located on the Power Conversion PCB. The A/D
converter shares the four-line, serial-communication interface with the D/A
converter. If the System microprocessor indicates that the energy stored is
out of tolerance, an ENERGY FAULT message is displayed.
I/O Protection. Electrostatic discharge protection is provided by the
resistors and capacitors on all the I/O lines that connect to the Main PCB.
Additional
protection is provided by 6.2V zener diodes, CR7 through CR9,
on the Video 1, Video 2, and Raster lines directed to the Monitor PCB.
Display/Recorder Controller. The central component of this circuit is the
Display/Recorder microprocessor U1. It receives the digitized ECG signal
data from the System microprocessor and controls the input of this data to the
Display PCB Assembly CRT and the recorder. Because the CRT screen
resolution is not as high as the recorder resolution, the Display/Recorder
microprocessor compresses ECG data for the CRT display. The recorder
receives all incoming ECG data samples. The Display/Recorder
microprocessor also formats the ECG data for the CRT so waveforms are not
displayed with gaps or overlapping segments.
ECG sample data is transmitted from the System microprocessor to the
Display/Recorder microprocessor through the Tx serial communication line
approximately every 1.8ms. Other data/command bytes from the System
microprocessor are also transmitted to the Display/Recorder microprocessor
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