Input/Output (I/O) Ports (PORTS)
NOTE:
Avoid glitches on port C pins by writing to the port C data register before changing
data direction register C bits from 0 to 1.
Figure 10-10 shows the port C I/O logic.
READ DDRC ($0006)
WRITE DDRC ($0006)
DDRCx
RESET
WRITE PTC ($0002)
READ PTC ($0002)
PTCx
PTCx
Figure 10-10. Port C I/O Circuit
When bit DDRCx is a logic 1, reading address $0002 reads the PTCx data latch.
When bit DDRCx is a logic 0, reading address $0002 reads the voltage level on the
pin. The data latch can always be written, regardless of the state of its data
direction bit. Table 10-3 summarizes the operation of the port C pins.
Table 10-3. Port C Pin Functions
Accesses
Accesses to PTC
DDRC
Bit
to DDRC
Read/Write
DDRC[6:0]
DDRC[6:0]
PTC Bit
I/O Pin Mode
Read
Pin
Write
X(1)
X
Input, Hi-Z(2)
Output
PTC[6:0](3)
PTC[6:0]
0
1
PTC[6:0]
1. X = don’t care
2. Hi-Z = high impedance
3. Writing affects data register, but does not affect input.
Data Sheet
118
MC68HC908MR32 • MC68HC908MR16 — Rev. 6.0
Input/Output (I/O) Ports (PORTS) MOTOROLA
FREESCALE [ Freescale ]
