MC68F375
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
5-8
when the CPU is operating in supervisor mode. Assignable data space can have either
restricted to supervisor-only data space access or unrestricted supervisor and user
data space accesses. The SUPV bit in QADC64MCR designates the assignable
space as supervisor or unrestricted.
Attempts to read or write supervisor-only data space when the CPU is not in supervisor
mode cause the bus master to assert the internal transfer error acknowledge (TEA)
signal.
The supervisor-only data space segment contains the QADC64 global registers, which
include QADC64MCR and QADC64INT. The supervisor/unrestricted space designa-
tion for the CCW table, the result word table, and the remaining QADC64 registers is
programmable.
5.6 General-Purpose I/O Port Operation
QADC64 port pins, when used as general-purpose input, are conditioned by a syn-
chronizer with an enable feature. The synchronizer is not enabled until the QADC64
decodes an IMB bus cycle which addresses the port data register to minimize the high-
current effect of mid-level signals on the inputs used for analog signals. Digital input
signals must meet the input low voltage (VIL) or input high voltage (VIH) requirements,
input pin does not meet the digital input pin specifications when a digital port read
operation occurs, an indeterminate state is read. To avoid reading inappropriate val-
ues on analog inputs, the user software should employ a “masking” operation.
During a port data register read, the actual value of the pin is reported when its corre-
sponding bit in the data direction register defines the pin to be an input (port A only).
When the data direction bit specifies the pin to be an output, the content of the port
data register is read. By reading the latch which drives the output pin, software instruc-
tions (like bit manipulation instructions) that read data, modify it, and write the result
work correctly.
There is one special case to consider for digital I/O port operation. When the MUX
(externally multiplexed) bit is set in QACR0, the data direction register settings are
ignored for the bits corresponding to PQA[2:0] and the three multiplexed address
MA[2:0] output pins. The MA[2:0] pins are forced to be digital outputs, regardless of
the data direction setting, and the multiplexed address outputs are driven. The data
returned during a port data register read is the value of the multiplexed address latches
which drive MA[2:0], regardless of the data direction setting.
5.6.1 Port Data Register
QADC64 ports A and B are accessed through two 8-bit port data registers (PORTQA
and PORTQB). Port A pins are referred to as PQA when used as an 8-bit input/output
port. Port A can also be used for analog inputs AN[59:52] and external multiplexer
address outputs MA[2:0].
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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