Mallinckrodt NELLCOR NPB-4000, Service Manual

Page: 116 / 219

Section 13: Microprocessor Computer and Control –Theory of Operation
13-2
The SpO
2
unit (MP-205) is connected to an asynchronous serial port via opto-
isolators.
The push switches and rotating knob interface to the 386EX via the FPGA
circuit. They are polled by the software at a 200-Hz rate.
The speaker is connected to an amplifier circuit, that is connected to a digital
potentiometer. The programmable frequency is generated in the FPGA and
connects to this programmable digital pot. The software controls the volume by
programming this digital pot.
The defib sync pulse is bit-programmed via software and goes to the outside
world via a digital driver.
The NIBP circuit is controlled by various port bits and control circuits in the
ASIC.
13.2 POWER SUPPLY CONNECTIONS
Figure 13-1: Power Supply Interface
See Figure 13-1. The power supply system provides the power for the main
board and all of the circuitry in the system. It also contains control circuits for
turning on and off the power, as well as supplying the battery backup for the
system.
13.2.1 Voltages
The microprocessor and its associated circuits are powered from the regulated
3.3 volts generated on the power supply board. The 3.3 volts powers the
microcontroller, DRAM, flash, LCD controller and a portion of the LCD
contrast circuit, memory, the DUART, and real-time clock. The 5 volts powers
the Nellcor knob, A/D converter, a portion of the LCD contrast circuit, and a
portion of the speaker circuit. The 12 volts powers portions of the LCD contrast
circuit and speaker circuit, the backlight inverter input voltage, and the op amp
for the battery voltage and temperature-monitoring signals going to the A/D
converter. The -24 volts is used to drive the LCD contrast regulator.