Mallinckrodt NELLCOR NPB-4000 Service Manual page 142

Section 14: Main Color Board Digital Theory of Operation
14-2
A RTC (real time clock) chip keeps the date and time of day. This unit has 64
bytes of battery backed up ram, 14 bytes are used for the RTC, and 50 bytes are
available for the software to use.
The recorder (thermal printer) and the external RS-232 port are controlled from
software via a DUART (dual serial port chip). These ports are the same as the
COM ports used on a PC and the DUART is programmable via software.
The SpO unit (MP205) is connected to one of the 386EX' s asynchronous serial
2
ports via opto-isolators.
The push buttons 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 which is connected to a digital
potentiometer. The programmable frequency is generated in the FPGA and
connects to this programmable digital potentiometer. 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 DEFIB SYNC pulse' s purpose is to indicate on
the leading edge that now is the time to fire the defibrillator.
The NIBP circuit is controlled by various port bits and control circuits in the
ASIC. It automatically inflates a pressure cuff attached to the patient and then
deflates the cuff and takes the measurement.
The main board uses the following voltages and nominal currents; 3.3 volts DC
at 300 mA, 5 volts DC at 260 mA, 12 volts DC at 315 mA with 165 mA for the
backlight, and -24 volts DC at 1.2 mA.
The IC' s and their reference designations are as follows:
386EX, U7
40MHZ OSC, X3
A/D CONV, U53
AUDIO POT, U26
BOOT FLASH, U504
CONTRAST POT, U18
DATA BUS BUFFER, U9
DRAM, U501
DRAM ADR MUX, U2,U6,U8
DUART, U24
FPGA, U505
LCD CONTROLLER, U500
LCD VRAM, U502
MISC BFRS, U1,U12,U17
OP AMPS, U27,U16,U25
PRSR XDCRS, PS1,PS2
RS232 BFR, U19
RTC, U4
RTC ADR MUX, U3
TREND FLASH, U14
VOLTAGE REG, VR1