GENERAL PURPOSE I/O CONFIGURATION
MOTOROLA
PORT B
5 - 5
If a pin is configured as a GPIO
output
and the processor reads the PBD, the processor
sees the contents of the PBD rather the logic level on the pin, which allows the PBD to be
used as a general purpose 15-bit register. If the processor writes to the PBD, the data is
latched there and appears on the pin during the following instruction cycle (see
5.2.2 Port B General Purpose I/O Timing
).
If a pin is configured as a
host
pin, the Port B GPIO registers can be used to help in
debugging the HI. If the PBDDR bit for a given pin is cleared (configured as an input), the
PBD will show the logic level on the pin, regardless of whether the HI function is using the
pin as an input or an output.
If the PBDDR is set (configured as an output) for a given pin that is configured as a
host
pin, when the processor reads the PBD, it sees the contents of the PBD rather than the
logic level on the pin - another case which allows the PBD to act as a general purpose
register.
Note:
The external host processor should be carefully synchronized to the DSP56002 to
assure that the DSP and the external host will properly read status bits transmitted
between them. There is more discussion of such port usage considerations in sec-
tions
Section 5.3.2.7 Host Port Usage Considerations – DSP Side
5.3.6.5 Host Port Usage Considerations – Host Side
5.2.1
Programming General Purpose I/O
Port B is a memory-mapped peripheral as are all of the DSP56002 peripherals (see
Figure 5-5). The standard MOVE instruction transfers data between Port B and a reg-
ister; as a result, MOVE takes two instructions to perform a memory-to-memory data
P
O
R
T
B
PB0
PB1
PB2
PB3
PB4
PB5
PB6
PB7
PB8
PB9
PB10
PB11
PB12
PB13
PB14
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BC0/BC1
BD0
BD1
BD2
BD3
BD4
BD5
BD6
BD7
BD8
BD9
BD10
BD11
BD12
BD13
BD14
ENABLED BY
BITS IN
X:$FFE0
DIRECTION
SELECTED BY
X:$FFE2
PB0
PB1
PB2
PB3
PB4
PB5
PB6
PB7
PB8
PB9
PB10
PB11
PB12
PB13
PB14
INPUT/OUTPUT
DATA
X:$FFE4
Figure 5-3 Parallel Port B Pinout
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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