Mallinckrodt NELLCOR NPB-4000, Service Manual

Page: 197 / 219

Section 16: MP-205 Service Manual; 044540A-0296
16-5
16.14 Power Decoupling
The power supply decoupling circuit consists of R29, R30, C16 through C18,
C28, and C26 and C27.
16.15 Status and Timing
The LED drive, ALC, demodulator, and demultiplexer require timing signals to
operate properly. All of the proper timing sequences are provided by the state
machine, the OXICLK signal, within the
Oxichip U1 circuit. The state machine
requires a clock from the CPU at 8 times the desired LED strobe frequency.
16.16 Analog Power Regulation
The oximetry module analog functions are powered by
±
5 volts DC. Analog
filtering is provided by R15 and R16, and C11 and C12.
16.17 Microcontroller
The oximetry module microcontroller is an 80C552 IC, U4, with 64K ROM, U3,
32K RAM, U7, and an address latch U6. The connection to the
Oxichip circuit
gain settings is through the data bus and the control lines CS* and LE.
Table 16-1: Oxichip Circuit Pin Descriptions
Pin Name
Pin #,
type
Signal Description
CS* 1, DI Chip Select, latches the data bus into the storage
registers.
Connected to WR* U4P3-6
LE 2, DI Latch Enable, enables writing to the storage register.
Connected to U4.P1-1
CYCLE 3, DO Indicates whether the Oxichip circuit is in a Red or IR
cycle.
High is Red, low is IR
Connected to U4P3-3
CLH 4, LP High side current limit protection
Connects to LED supply voltage through resistor R10
in parallel with capacitor C9.
LEDPOS 5, LO +LED connection to sensor
LEDNEG 6, LO -LED connection to sensor
CLL 7, LP Low side current control. Connects to LED supply
return through 10 Watt resistor R9.
GATE 8, DO Combined gate signal, rising edge initiates a
COMPARE A/D conversion.
Connects to U4-STADC
SATIN* 9, DO LED on or off status indicator: high is off, low is on.
Connects to U3P4-3.
RESET* 10, DI Input of Schmitt Trigger for generating a reset.
RST 11, DO Output of Schmitt Trigger, active high reset pulse.
VSS 12, DP Digital power return.