Chapter 9: Service Maintenance and Repair
9-2
Oximeter Operation and Service Manual
Memory address map is shown in the following table:
Display Select Signal DSP-LD is used to latch displayed data into U22 and
U23 LED drivers.
Address decoder for Input/Output Interface devices is implemented using
U17B demultiplexer chip.
The I/O address space is divided according to the following table:
Watch dog timer U18 is used to reset microprocessor in case of ESD and at
power up. Its internal comparator is used to compare battery voltage offset
by Vr voltage coming from digitally controlled potentiometer with internal
U18 voltage reference. The output of the comparator (signal BATT) is used
to detect battery voltage. The following battery states are distinguished by
this measurement system:
RS-232 communication interface is built around Q3, Q5, and Q6. It con-
verts CMOS voltage levels into RS-232 bipolar voltage levels. Inverter
U16C is used to disable communication interface circuitry when oximetry
probe is plugged in to reduce power consumption and eliminate cross-talk
between communication and probe reading.
Device
Address Space
OTP ROM
0..FFFF
RAM
10000..1FFFF
Display Select Signal
20000..2FFFF
I/O Address Space
Device
0..3F
Used by Z180 for internal registers
40..7F
Input port
80..BF
Output port
Battery Voltage
Condition
2.7V
Dead battery level-units shuts itself
off
3.0V
Low battery level-signal to user
4.5V
Ok battery level
Содержание 1818R
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