Novametrix Medical Systems OXYPLETH 520A, Service Manual

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2471 & 2775 Main Board
5-Jun-01 Model 520A Service Manual
33
PRELIMINARY
After receiving the correct number of bits for the ADC being read, the CPU changes
the AA1 and AA0 decode lines and exerts the Next line (NEXT*) at IC18 pin 9 low.
This restarts the serial data shifting out of the newly selected ADC.
After all three ADCs have been read, the CPU sets the AA1 and AA0 decode lines
to exert the internal TEND signal and set the 8-bit ADC to the next channel (so that
it has time to settle before the next read of the ADC). This re-enables the CPUINIT
line. At this point the CSI/O controller is reset awaiting an INT5MS pulse to begin
the cycle again.
RS232 Serial Communication
9.3.23
The Model 520A supports serial (RS232) communication with external devices via
the monitor’s rear panel connector. Signals to and from the rear panel RS232
connector are electrically isolated from the rest of the Model 520A electronics by
four opto-isolators (IC3-IC6). (See sheet 5 on 2471 schematic, sheet 4 on 2775
schematic.)
An isolated secondary coil from transformer T1 is rectified and filtered by D1 and
C1 before being input to the +5 volt regulator IC2. The regulated output of IC2 is
sent to pin 25 of the 25-pin D connector on the rear panel in order to power the
optional Analog Module or Telemetry transmitter. The supply also powers IC1.
The Dual RS232 Transmitter/Receiver, IC1, uses a 5 volt supply (pin 16).
The two Receive (Rx) inputs can accept
±
30 volt levels, while the two Transmit
(Tx) lines output
±
9 volt levels. The four level translators within the chip turn the
RS232 level signals to 5 volt TTL/CMOS compatible levels.
Two signals lines TX0 and TX1 transmit data from the CPU across the opto-
isolators ICs 3 and 4 to IC1. Here the signals are level shifted to the standard
±
9 volt
levels and sent to the rear panel connector.
When the CPU brings the TX0 signal at R62 Low, the LED portion of IC3 becomes
forward biased and illuminates and causes the transistor portion of the device to
conduct. Therefore, when TX0 is Low, IC1 pin 11 is Low and when TX0 is High,
IC1 pin 11 is also High. All four opto-isolators work in the same way. IC1 level
shifts its input at pin 11 and outputs RS232 standard
±
9 volt levels at the TX signal
at J101 pin 3. This transmit signal is used to output data to RS232 devices including
the Hewlett-Packard ThinkJet Printer and the Novametrix Model 315 Printer.
The CPU TX1 signal crosses the isolation barrier at IC4. The 0-5 volt opto-isolator
output at IC4 pin 5 is used to bring data to the Optional 9622-01 Analog Module.
The IC4 pin 5 output is also brought to IC1 pin 10. The level shifted output at IC1
pin 7 is unused (except for factory test use).
The Receive (RX) line at J101 pin 2 and the Clear To Send (CTS) line at J101 pin
6 are input signals to the Model 520A. They are level shifted by IC1 and sent across
the isolation barrier by ICs5 and 6 respectively.