Philips M3921A Service Manual page 137

Theory of Operation and System Architecture
RS-232 I/O
This is a rear panel 9-pin connector providing interfaces with other computer
systems or equipment. The driver for this "port" is a Universal Asynchronous
Receive-Transmit (UART) integrated circuit that interfaces this port with the
microprocessor. The baud rate for this serial transmission function is
programmable from 1200 baud to 38.4 kilobaud.
Pin number 9 of the RS-232 connector is reserved for a Nurse Call signal. The
nurse call signal reacts when a low, medium, or high level alarm is activated.
Defib Sync Pulse
The rear panel connector for the Defib Sync Pulse is keyed so that the
connection of a cable can be detected by the processor. When a connection is
detected, the processor software initiates the generation by hardware of a
TTL-compatible pulse capable of driving 1 TTL load over a three-meter cable
with less that 200 pF capacitance.
The defib pulse is triggered by the detection of the R-wave in the QRS
sequence of the ECG wave-form complex. The pulse signal is active for 100
±10 ms.
Speaker
The speaker is capable of providing 73 dBA of volume at a distance of one
meter during alarm conditions. The processor drives the speaker in different
patterns as specified for the different alarm priorities and conditions. Refer to
the operator's manual for descriptions of alarm responses.
Recorder
The optional recorder module is installed in the right panel of the monitor.
Refer to the User Guide for printing procedures. It provides users with the
capability to obtain hard-copy records of selected vital signs information.
Basic control of the recorder is implemented by two push-switch controls on
the recorder front panel. One of these is used to obtain continuous recordings
of the real-time waveforms displayed in the top two graphic frames. Along
with the waveforms, the recorder prints the values of the vital signs being
displayed. The printing continues until the user presses either recorder switch
a second time.
The other control switch initiates a printout for 20 seconds of the same
information recorded by the continuous control.
If scrolling is enabled in a display frame containing trend data when the
continuous recording switch is operated, then the trend record for that vital
sign is printed. If the snapshot recording switch is operated, then only the
trend data on the display is printed.
The recorder may be programmed via the monitor menu display to print a
snapshot recording when an alarm condition occurs.
Chapter 10 - Training Program 125