Mallinckrodt NELLCOR NPB-4000 Service Manual page 91

10.2.4 µP, Memory, and Control
10.2.5 Display
10.2.6 Keypad (Switches) and Knob
The microprocessor (µP), Memory, and Control section contains the system CPU
and all digital support circuitry. The latter includes the RAM, nonvolatile
memory, and real-time clock. This section also contains the display logic,
keypad (switch) interface logic, RS-232 I/O control, defibrillator synchronization
control, and printer logic.
The display is a cold-cathode, backlighted, fluorescent LCD unit. The pixel
resolution of 0.23 mm provides a 640x480 line display. The NPB-4000 display
is presented in black and white mode only (no gray scale). The NPB-4000C
display is presented in color.
The keypad circuit contains five push-switch membrane switches and two green
LEDs. The LEDs are driven by the power supply system and indicate the source
of externally applied power mains (AC or DC), the charging of the batteries, and
the condition of the source cable in-line fuses. Signals from the LEDs are
returned to the microcomputer for processing and control as required.
The power switch, connected directly to the supply, toggles the power between
Standby and On modes. When in Standby, the display is blank, and no
monitoring is performed. However, the batteries are charging if either an AC or
DC power source is connected to the rear panel.
The alarm silencing switch is connected directly to the processor and to the
system power supply. Pressing this switch turns off the battery fuse alarm in the
system power supply. Response of the processor depends upon the action in
pressing this switch. If momentarily pressed (less than 2 seconds), alarms are
silenced temporarily for a preset interval determined by the menu selection. If
held pressed for 2 seconds or more, the Alarm Suspend condition is initiated.
The NIBP switch output is connected to the processor. Response of the
processor depends upon the state of NIBP operation at the time and the action in
pressing this switch. If momentarily pressed (less than 2 seconds), a single NIBP
measurement is obtained. If pressed for 2 seconds or more, the processor
initiates a STAT monitoring sequence. Pressing the NIBP switch at any time a
pressure measurement is in effect will cause the processor to terminate the
measurement and to deflate the cuff.
NPB-4000. The display Contrast switch, operates in conjunction with the
Nellcor knob to determine the apparent black/white contrast setting in the
display. Changing contrast is actually a change in the viewing angle. Outputs
of the switch and knob are connected to the processor. Momentary pressing the
switch sets the contrast to mid-range, factory-default value. Momentary
pressing the switch, followed within 3 seconds by a rotation of the knob, are
processed to vary the contrast of the display. When there has been no knob
rotation for three seconds, the contrast control function is terminated by the
processor. The contrast control function also is terminated if the knob is
pressed any time within this 3-second interval.
Section 10: Introduction and System Description
10-3