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• A 5 channel 8 bit A/D converter used for battery management and to measure
the pcb temperature
6.3
CPU Memory
Flash PROM - (ICI 5)
An 8Mbit programmable ROM which is capable of being written to while still in
circuit. Contains all the main command software for the HHP
Static Random Access Memory (SRAM) - (IC9)
A 16 bit (64k by 16) temporary memory device which is used by NELL for CPU
program execution.
EEPROM - (IC10)
A 4Kbyte electrically erasable and programmable ROM, which communicates via
the EECLK / EEDAT (#5-6) lines to NELL. It contains all the user memories and
calibration data.
The location of these devices relative to NELL can be seen in Figure 10b.
6.4 Battery Interface and Power Supply
6.4.1 Battery Monitors and PCB Temperature Interface
The HHP can monitor the state of the battery through the battery interface
connector P8. This can be done during both normal and charging operations. The
battery provides a number of interface connections that enable the HHP to
determine the battery type, its capacity, temperature and whether it is possible to
re-charge the cell(s). The thermister (R124) which is attached to the logic board
pcb is used to produce an analogue reading of the board's own surface
temperature. The P8 connector provides a connection between the battery power
contacts VBAT/GND to the RF board and BATTEMPMON/BATID battery monitoring
circuits to the battery. IC30 #2 provides the bias/reference supply: VREF for these
analogue monitors and is also fed to IC29.
Battery voltage monitoring (BATVMON) is performed by the circuit:IC30/IC29, with
the output of the regulator IC30 #2 feeding the comparator IC29 #3. IC29 uses
this input as a stabilised voltage reference level, which it compares to VBAT to
produce the analogue output BATVMON. This output is then supplied to NELL
#M9 for A/D conversion. BATVMON enables the HHP to measure the battery
voltage and hence determine how much charge remains in the cells.
The remainder of the analogue inputs from these circuits are also fed to NELL for
A/D conversion.
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