MC68HC705JP7 Datasheet, PDF (138/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog Subsystem
8.9 Current Source Features
The internal current source connected to the PB0/AN0 pin supplies
about 100 µA of current when the discharge device is disabled and the
current source is active. Therefore, this current source can be used in an
application if the ISEN enable bit is set to power up the current source
and by setting the A/D conversion method to manual mode 0 (ATD1 and
ATD2 cleared) and the charge current enabled (CHG set).
8.10 Internal Temperature Sensing Diode Features
An internal diode is forward biased to V_SS and will have its voltage
change, V_D, for each degree centigrade rise in the temperature of the
device. This temperature sensing diode is powered up from a current
source only during the time that the diode is selected. When on, this
current source typically adds about 30 µA to the I_DD current.
The temperature sensing diode can be selected by setting both the
HOLD and DHOLD bits in the AMUX register (see 8.3 Analog Multiplex
Register).
8.11 Sample and Hold
When using the internal sample capacitor to capture a voltage for later
conversion, the HOLD or DHOLD bit must be cleared first before
changing any channel selection. If both the HOLD (or DHOLD) bit and
the channel selection are changed on the same write cycle, the sample
may be corrupted during the switching transitions.
NOTE:
The sample capacitor can be affected by excessive noise created with
respect to the device’s V_SS pin such that it may appear to leak down or
charge up depending on the voltage level stored on the sample
capacitor. It is recommended to avoid switching large currents through
the port pins while a voltage is to remain stored on the sample capacitor.
The additional option of adding an offset voltage to the bottom of the
sample capacitor allows unknown voltages near V_SS to be sampled and
then shifted up past the comparator offset and the device offset caused
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MC68HC705JJ7 • MC68HC705JP7 — REV 4
Analog Subsystem
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