Chapter 21 Multiplexed External Bus Interface (MEBIV3)
MC9S12HZ256 Data Sheet, Rev. 2.05
Freescale Semiconductor
581
Read: Anytime when register is in the map
Write: Anytime when register is in the map
Port A bits 7 through 0 are associated with address lines A15 through A8 respectively and data lines
D15/D7 through D8/D0 respectively. When this port is not used for external addresses such as in
single-chip mode, these pins can be used as general-purpose I/O. Data direction register A (DDRA)
determines the primary direction of each pin. DDRA also determines the source of data for a read of
PORTA.
This register is not in the on-chip memory map in expanded and special peripheral modes. Therefore, these
accesses will be echoed externally.
NOTE
To ensure that you read the value present on the PORTA pins, always wait
at least one cycle after writing to the DDRA register before reading from the
PORTA register.
21.3.2.2
Port B Data Register (PORTB)
Read: Anytime when register is in the map
Write: Anytime when register is in the map
Port B bits 7 through 0 are associated with address lines A7 through A0 respectively and data lines D7
through D0 respectively. When this port is not used for external addresses, such as in single-chip mode,
these pins can be used as general-purpose I/O. Data direction register B (DDRB) determines the primary
direction of each pin. DDRB also determines the source of data for a read of PORTB.
This register is not in the on-chip memory map in expanded and special peripheral modes. Therefore, these
accesses will be echoed externally.
NOTE
To ensure that you read the value present on the PORTB pins, always wait
at least one cycle after writing to the DDRB register before reading from the
PORTB register.
76543210
R
Bit 7
6
5
4
3
2
1
Bit 0
W
Reset
0
Single Chip
PB7
PB6
PB5
PB4
PB3
PB2
PB1
PB0
Expanded Wide,
Emulation Narrow with
IVIS, and Peripheral
AB/DB7
AB/DB6
AB/DB5
AB/DB4
AB/DB3
AB/DB2
AB/DB1
AB/DB0
Expanded Narrow
AB7
AB6
AB5
AB4
AB3
AB2
AB1
AB0
Figure 21-3. Port A Data Register (PORTB)