Figure 9-14: N-20 Hardware Block Diagram - Mallinckrodt Nellcor N-20 Service Manual

Technical Supplement
Interface
Patient
Sensor
Output
Battery
Type
Lithium
Battery
External to Board
BUSSES
SIGNALS
The CPU has the ability to dynamically switch the data bus width—based on the BUSWIDTH input
pin. A low on BUSWIDTH tells the CPU to access memory only 8 bits at a time. When accessing
the static RAM, BUSWIDTH is low, automatically reading the 8-bit wide RAM. Since BUSWIDTH
is connected to the active low RAM enable line (RAMEN), all other memory and mapped I/O are read
or written 16 bits at a time.
The CPU measures eight analog inputs. Input from the SpO
signals for the oximeter sensor red and infrared channels, and the sensor calibration resistor RSENS.
Light, temperature, and battery voltage are also measured.
9-14
Analog
Ambient
Reference
Voltage
Serial
Control
SpO2
Analog
Analog
Section
Address
Decoding
AD Bus
Enables
Input
Port Port
Input Port
Output Port
Real Time
Audio
Clock and
Output
Non-Volatile
Memory

Figure 9-14: N-20 Hardware Block Diagram

Battery
Light Voltage
C P U
Control AD Bus
Address
Demultiplexing
CPU
Memory
Digital I/O
Display
Control
User
Display
analog section includes AC and DC
2
Ambient
Temperature
Analog
Battery
Power
Power
Off Power
Control
Power
Control
Power
Supply
Standard
User
Supply
Digital I/O
Printer
Interface
User
Controls
Optional Printer
Flex Circuit with
User Controls