
MOTOROLA
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MC68336/376
8-4
USER’S MANUAL
8.4.1.1 Port A Analog Input Pins
When used as analog inputs, the eight port A pins are referred to as AN[59:52]. Due
to the digital output drivers associated with port A, the analog characteristics of port A
are different from those of port B. All of the analog signal input pins may be used for
at least one other purpose.
8.4.1.2 Port A Digital Input/Output Pins
Port A pins are referred to as PQA[7:0] when used as a bidirectional 8-bit digital input/
output port. These eight pins may be used for general-purpose digital input signals or
digital open drain pull-down output signals.
Port A pins are connected to a digital input synchronizer during reads and may be used
as general purpose digital inputs.
Each port A pin is configured as an input or output by programming the port data
direction register (DDRQA). Digital input signal states are read from the PORTQA data
register when DDRQA specifies that the pins are inputs. Digital data in PORTQA is
driven onto the port A pins when the corresponding bits in DDRQA specify outputs.
Refer to D.5.5 Port Data Direction Register for more information. Since the outputs
are open drain drivers (so as to minimize the effects to the analog function of the pins),
external pull-up resistors must be used when port A pins are used to drive another de-
vice.
8.4.2 Port B Pin Functions
The eight port B pins can be used as analog inputs, or as an 8-bit digital input only port.
Refer to the following paragraphs for more information.
8.4.2.1 Port B Analog Input Pins
When used as analog inputs, the eight port B pins are referred to as AN[51:48]/
AN[3:0]. Since port B functions as analog and digital input only, the analog character-
istics are different from those of port A. Refer to APPENDIX A ELECTRICAL CHAR-
ACTERISTICS for more information on analog signal characteristics. All of the analog
signal input pins may be used for at least one other purpose.
8.4.2.2 Port B Digital Input Pins
Port B pins are referred to as PQB[7:0] when used as an 8-bit digital input only port.
In addition to functioning as analog input pins, the port B pins are also connected to
the input of a synchronizer during reads and may be used as general-purpose digital
inputs.
Since port B pins are input only, there is no associated data direction register. Digital
input signal states are read from the PORTQB data register. Refer to D.5.5 Port Data
Direction Register for more information.
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