Port B - Motorola DragonBall MC68328 User Manual

Parallel Ports
bits are associated with each port pin: data, direction, and select. Bit "n" of each register byte
controls its associated pin function. The programmer's model for port A is:
15 14 13 12
DIRECTION
DIR7 DIR6 DIR5 DIR4
Address: $FFFFF400
15 14 13 12
0 0 0 0
Address: $FFFFF402
DIRECTION- DIR[7:0]
These bits control the pin directions. While high, the pins are outputs; while low, the pins
are inputs. These bits reset to 0 and have no function while the SELECT bits are low.
DATA- D[7:0]
These bits control or report the data on the pins while the associated SELECT bits are
high. While the DIRECTION bits are high (output), D[7:0] controls the data to the pins.
While the DIRECTION bits are low (input), D[7:0] reports the signal level on the pins. The
data bits may be written at any time. Bits that are configured as inputs will accept the data,
but the written data will not be accessible until their respective pins are configured as out-
puts. The actual value on the pin is reported when these bits are read regardless of wheth-
er they are configured as input or output. These bits reset to 0 while the SELECT bits are
low.
SELECT- SEL[7:0]
These bits select whether address [23:16] or I/O port signals are connected to the pins.
While high, the port I/O functions are connected to the pin. While low, the address function
is connected.

7.1.3 Port B

Port B is multiplexed with data lines D7-D0. In an 8-bit-only system, these pins can be con-
figured as a parallel port. However, the boot-up sequence must configure port B as I/O. This
port is not affected by the BUSW pin. On reset, the data lines are connected to the pins. The
programmer's model for Port B is:
15 14 13 12
DIRECTION
DIR7 DIR6 DIR5 DIR4
Address: $FFFFF408
7-4 MC68328 DRAGONBALL PROCESSOR USER'S MANUAL
11 10 9
DIR3 DIR2 DIR1
Figure 7-4. Port A Data/Direction Register
11 10 9
UNUSED
0 0 0
Figure 7-5. Port A Select Register
11 10 9
DIR3 DIR2 DIR1
Figure 7-6. Port B Data/Direction Register
8 7 6 5
DIR0 D7 D6 D5
8 7 6 5
0 SEL7 SEL6 SEL5
8 7 6 5
DIR0 D7 D6 D5
4 3 2 1
DATA
D4 D3 D2 D1
Reset Value: $0000
4 3 2 1
SELECT
SEL4 SEL3 SEL2 SEL1
Reset Value: $0000
4 3 2 1
DATA
D4 D3 D2 D1
Reset Value: $0000
MOTOROLA
0
D0
0
SEL0
0
D0