Mallinckrodt NELLCOR NPB-4000 Service Manual page 92

Section 10: Introduction and System Description
10.2.7 Nellcor Knob
10.2.8 RS-232 I/O
10.2.9 Defib Synch Pulse
10.2.10 Speaker
10-4
NPB-4000C. Pressing the Contrast switch changes the background color from
white to black or black to white.
Operation of the Volume switch accomplishes similar functions for the volume
of the heart rate audible tone as the display contrast control switch does for the
display. Pressing this switch enables the knob to vary the tone volume. The
same timing consideration of 3 seconds is provided, in which to adjust the tone
volume or to terminate the action.
This is a rotating, push-switch knob. The associated knob circuitry generates a
pulse when pressed and generates a digitally encoded pair of quadrature signals
whose relative magnitudes and polarities represent the angular position of the
knob. These outputs are connected to the processor where they are interpreted as
required for the functions involved. Successive angular positions determine the
direction of knob rotation.
In addition to the functions performed when in conjunction with the keypad
switches as described above, the Knob operates in conjunction with the display
to select menus and lists of parameter variables.
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.
One pin (9) of 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.
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 than 200 pF capacitance.
The defib pulse is triggered by the detection of the R-wave in the QRS sequence
of the ECG waveform complex. The pulse signal is active for 100±10
milliseconds.
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.