mc9s12c32mpb16 Freescale Semiconductor, Inc, mc9s12c32mpb16 Datasheet - Page 150

• Manufacturer Part Number: mc9s12c32mpb16
• Description: Hcs12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 4 Multiplexed External Bus Interface (MEBIV3)
4.3.2.16
Read: Anytime
Write: Anytime
This register determines the primary direction for each port K pin configured as general-purpose I/O. This
register is not in the map in peripheral or expanded modes while the EMK control bit in MODE register is
set. Therefore, these accesses will be echoed externally.
4.4
4.4.1
The external signals LSTRB, R/W, and AB0 indicate the type of bus access that is taking place. Accesses
to the internal RAM module are the only type of access that would produce LSTRB = AB0 = 1, because
the internal RAM is specifically designed to allow misaligned 16-bit accesses in a single cycle. In these
cases the data for the address that was accessed is on the low half of the data bus and the data for
address + 1 is on the high half of the data bus. This is summarized in
150
Module Base + 0x0033
Starting address location affected by INITRG register setting.
DDRK
Field
7:0
Reset
W
R
Functional Description
Detecting Access Type from External Signals
Data Direction Port K Bits
0 Associated pin is a high-impedance input
1 Associated pin is an output
Note: It is unwise to write PORTK and DDRK as a word access. If you are changing port K pins from inputs to
Note: To ensure that you read the correct value from the PORTK pins, always wait at least one cycle after writing
Port K Data Direction Register (DDRK)
Bit 7
0
7
outputs, the data may have extra transitions during the write. It is best to initialize PORTK before enabling
as outputs.
to the DDRK register before reading from the PORTK register.
LSTRB
1
0
1
0
Figure 4-20. Port K Data Direction Register (DDRK)
6
0
6
Table 4-15. Access Type vs. Bus Control Pins
AB0
Table 4-14. EBICTL Field Descriptions
0
1
0
1
MC9S12C-Family / MC9S12GC-Family
5
0
5
R/W
1
1
0
0
Rev 01.23
4
0
4
Description
8-bit read of an even address
8-bit read of an odd address
8-bit write of an even address
8-bit write of an odd address
3
3
0
Type of Access
Table
2
2
0
4-15.
Freescale Semiconductor
1
0
1
Bit 0
0
0