Mallinckrodt NELLCOR NPB-4000, Service Manual

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13-1
SECTION 13: MICROPROCESSOR COMPUTER AND CONTROL –
THEORY OF OPERATION
13.1 General
13.2 Power Supply Connections
13.3 NIBP Processing
13.4 Recorder Operation
13.5 Isolated Front End Power Interface
13.6 SpO
2
Interface
13.7 Isolated Front End Power Signals
13.8 RS-232 Serial Port Interface
13.9 CPU Connections
13.10 Knob Interface Control
13.11 Push Switch Control
13.12 Digital Schematic Pages 1/2
13.13 Current Drain of Digital Electronics
13. MICROPROCESSOR COMPUTER AND CONTROL –THEORY OF OPERATION
13.1 GENERAL
The NPB-4000/C digital design is based on an Intel 386EX microcontroller,
which has a 386SX microprocessor core and peripheral blocks around it. The
internal peripherals are all controlled by on-board programmable registers. In
order to save power, this design has a Vcc = 3.3 volts.
The data from the Front End (ECG, temp, resp) is multiplexed through a linear
opto isolator to a 12-bit A/D converter, which is connected to the on-board
synchronous serial port. The synchronous serial port is controlled by the
on-board DMA unit.
The LCD display is a 640x480 black and white display that is connected to an
S-MOS 1351FLB controller chip. This chip interfaces via the data bus to the
386EX. It has two 32kx8 SRAMs for data storage. The backlight is controlled
by en12 volts to the inverter board. The contrast for the LCD is
controlled from the onboard -24 volts.
The main executable memory is a 256Kx16 flash memory which takes the upper
512k bytes of address space. This flash contains the boot program and the
executable program for controlling the whole unit.
A 512-kbyte DRAM is located in lower memory starting at location 0 and is used
for data storage and manipulation. The DRAM also has the ability to execute
code when programming the flash with a new program from the external RS-232
port.
An RTC (real-time clock) chip is connected which keeps date and time of day.
This unit has 64 bytes of battery-backed-up RAM; 14 bytes are used for the
real-time clock (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.