mc68hc05jp6pe Freescale Semiconductor, Inc, mc68hc05jp6pe Datasheet - Page 135

• Manufacturer Part Number: mc68hc05jp6pe
• Description: M68hc05 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.12 Port B Interaction with Analog Inputs
8.13 Port B Pins as Inputs
MC68HC05JJ6/MC68HC05JP6
Freescale Semiconductor
NOTE:
The sample capacitor can be affected by excessive noise created with
respect to the device’s V
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
then shifted up past the comparator offset and the device offset caused
by a single V
the internal V
N
case, the proper mask option must be selected and the VOFF bit must
be set in the ASR. It is not necessary to switch the VOFF bit during
conversions, since the offset is controlled by the HOLD and DHOLD bits
when the VOFF is active. Refer to
more details on the design and decoding of the sample and hold circuit.
The analog subsystem is connected directly to the port B I/O pins without
any intervening gates. It is, therefore, possible to measure the voltages
on port B pins set as inputs or to have the analog voltage measurements
corrupted by port B pins set as outputs.
All the port B pins will power up as inputs or return to inputs after a reset
of the device, since the bits in the port B data direction register will be
reset.
If any port B pins are to be used for analog voltage measurements, they
should be left as inputs. In this case, not only can the voltage on the pin
be measured, but the logic state of the port B pins can be read from
location $0002.
OFF
—
Rev. 3.2
as described in
SS
SS
return pin. This offset also provides a means to measure
Analog Subsystem
level, regardless of the comparator offset, to determine
8.7 Voltage Measurement
SS
pin such that it may appear to leak down or
8.3 Analog Multiplex Register
General Release Specification
SS
Methods. In either
to be sampled and
Analog Subsystem
for
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