MC3S12RG128 Datasheet, PDF (138/546 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 4 Multiplexed External Bus Interface (MEBIV3) Block Description
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.
4.3.2.2 Port B Data Register (PORTB)
Module Base + 0x0001
Starting address location affected by INITRG register setting.
R
W
Reset
Single Chip
Expanded Wide,
Emulation Narrow with
IVIS, and Peripheral
Expanded Narrow
7
Bit 7
0
PB7
AB/DB7
AB7
6
5
4
3
6
5
4
3
0
0
0
0
PB6
PB5
PB4
PB3
AB/DB6 AB/DB5 AB/DB4 AB/DB3
AB6
AB5
AB4
AB3
Figure 4-4. Port A Data Register (PORTB)
2
2
0
PB2
AB/DB2
AB2
1
1
0
PB1
AB/DB1
AB1
0
Bit 0
0
PB0
AB/DB0
AB0
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.
MC3S12RG128 Data Sheet, Rev. 1.05
138
Freescale Semiconductor