Nellcor NPB-40 Service Manual page 38

Technical Supplement
S-6
From
batteries
Battery power
3.6-6 Vdc
From front
panel keypad
Power
switch
On/off
circuit
key
Power
shut off
control
Shift
key
Display light/
beep on/off
key
Store data/
print
key
WD
RST
VCC
monitor
and
watchdog
reset
circuit
10MHz
clock
circuit
Figure S3-2: CPU PCB Block Diagram
Battery power
feedback
Power
supply
circuit
Power on
Battery
voltage
sense
RD/WR
RAM
AD 0-7
RAM
enable
WR
Address
decoding
AD 0-15
Address
ALE
latch
AD 0-7
External
output
enable
Beeper drive
External
output
LCD light enable
port
LCD CLK,
DATA, CE
LCD enable
Printer LED signal
Analog sensor voltage reference
Analog sensor signal
Analog circuit control signal
To LCD PCB
Raw
+10 Vdc
Raw
-5 Vdc
VCC (+5 Vdc)
To CPU PCB circuits
ADDR
0-12
ADDR
9-15
EPROM enable
ADDR
1-15
EPROM
RD
AD 0-15
To/from LCD PCB
Beeper
LCD
backlight
LCD
driver
Printer
interface
V ref
Sensor
circuits