Datascope Passport - Mindray

CPU Control Module Theory of Operation
2.1.26 D/A Analog Outputs
There are two analog outputs for recreation of the ECG waveform and IBP measurement.
Both analog signals are created using a dual 12-bit D/A, U724 and Op-Amp, U701. The
required 4.096V reference is supplied by U638.
The ECG_OUT channel is composed of half of U701. The first stage is a low pass filter with
a gain of 2 and a level shift to allow a maximum output swing of ± 4.096V. The second
stage provides a gain of 1.25. The IBP_OUT channel is composed of half of U701. The first
stage is a low pass filter with a gain of 2 and a level shift to allow a maximum output swing
of ± 4.096V. The second stage provides a gain of 1.25 allowing the maximum amplitude to
be ± 5V. The dual 12 bit D/A converter gets its data from the Communications Processor's
SPI port qualified by PCS0. Clock and data to U724 are buffered by. The data is recreated
from measurement data received by the Communications Processor over the module bus.
2.1.27 Analog Inputs
2.1.28 SRAM
The communications Processor has a 6 channel A/D converter, only 4 channel are used at
this time. The A/D converter is only for monitoring voltages and not for critical
measurements. AN0 and AN1 are assigned to external analog inputs. There is an attenuator
circuit provided to keep the input to the A/D within its limits. AN3 and AN4 are assigned to
measure the internal battery voltages. They also have an attenuator circuit which attenuates
the battery voltage by 1/4, to stay within the limits of the A/D converter (5 Vdc).
There is 128K x 8 bytes SRAM which is used to store temporary variables and data required
by the Communications Processor.
2.1.29 Keypad and Rotary Knob
The front panel keypad is interfaced to the QSPI port qualified by PCS1. In order to read a
key, keypad scanning is used. The actual scanning logic is contained on the Interconnect
board, 0670-00-0686 and 0670-00-0714 in CPLD, U1. The keypad rows are exercised
with a Awalking zero pattern. This means that three out of four lines will always be at a logic
1 with one line driven low. In a complete cycle, each line will sequentially go low, driving a
different row on the keypad. This cycle is repeated continuously at a fast rate. The eight
columns are read, whenever a key is depressed, the coordinates of that key will be
determined by knowing which column line. The Communications Processor sends the scan
pattern on the QSPI port transmit output (MOSI) and receives the keypressed response on the
QSPI receive input (MISO). The QSPI signal are connected to the Interconnect board through
connector J5. The keypad connects to mating connectors on the Interconnect Board.
The front panel rotary selector is quadrature encoder with an integral switch. The purpose of
this device is for LCD menu scroll and selection. The quadrature signals CHA and CHB are
input from connector J5-70 and J5-71. The Communications Processor interprets the serial
data stream and sends it to the MPC860T through the Dual Port Ram, representing direction
and speed as well as the status of the integral switch.
2 - 10 0070-10-0441 Passport 2®/Passport 2 LT Service Manual