Freescale Semiconductor, Inc.
Ana log Sub syste m
8.8.2 Volta g e Com p a ra tor 2
Voltage comparator 2 can be used as a simple comparator if its charge
current source and discharge device are disabled by clearing the ISEN
bit in the ACR. If the ISEN bit is set, the internal ramp discharge device
connected to PB0/AN0 may become active and try to pull down any
voltage source that may be connected to that pin. Also, since voltage
comparator 2 is always connected to two of the port B I/O pins, these
pins should be configured as inputs and have their software
programmable pulldowns disabled.
8.9 Curre nt Sourc e Fe a ture s
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 Inte rna l Te m p e ra ture Se nsing Diod e Fe a ture s
An internal diode is forward biased to V and will have its voltage
SS
change approximately 2 mV 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 adds about 30 µA to the I current.
DD
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 Sa m p le a nd 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
General Release Specification
MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0
Analog Subsystem
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