Datasheet
I/O Registers
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor 197
12.8.1 PTC6/SCTxD (Transmit Data)
The PTC6/SCTxD pin is the serial data (standard or infrared) output from the SCI transmitter. The IRSCI
shares the PTC6/SCTxD pin with port C. When the IRSCI is enabled, the PTC6/SCTxD pin is an output
regardless of the state of the DDRC6 bit in data direction register C (DDRC).
NOTE
The PTC6/SCTxD pin is an open-drain pin when configured as an output.
Therefore, when configured as SCTxD or a general purpose output pin
(PTC6), a pullup resistor must be connected to this pin.
12.8.2 PTC7/SCRxD (Receive Data)
The PTC7/SCRxD pin is the serial data input to the IRSCI receiver. The IRSCI shares the PTC7/SCRxD
pin with port C. When the IRSCI is enabled, the PTC7/SCRxD pin is an input regardless of the state of
the DDRC7 bit in data direction register C (DDRC).
NOTE
The PTC7/SCRxD pin is an open-drain pin when configured as an output.
Therefore, when configured as a general purpose output pin (PTC7), a
pullup resistor must be connected to this pin.
Table 12-5 shows a summary of I/O pin functions when the SCI is enabled.
12.9 I/O Registers
The following I/O registers control and monitor SCI operation:
• IRSCI control register 1 (IRSCC1)
• IRSCI control register 2 (IRSCC2)
• IRSCI control register 3 (IRSCC3)
Table 12-5. SCI Pin Functions (Standard and Infrared)
IRSCC1
[ENSCI]
IRSCIRCR
[IREN]
IRSCC2
[TE]
IRSCC2
[RE]
TxD Pin RxD Pin
1000
Hi-Z
(1)
1. After completion of transmission in progress.
Input ignored (terminate externally)
1001
Hi-Z
(1)
Input sampled, pin should idle high
1 0 1 0 Output SCI (idle high) Input ignored (terminate externally)
1 0 1 1 Output SCI (idle high) Input sampled, pin should idle high
1100
Hi-Z
(1)
Input ignored (terminate externally)
1101
Hi-Z
(1)
Input sampled, pin should idle high
1 1 1 0 Output IR SCI (idle high) Input ignored (terminate externally)
1 1 1 1 Output IR SCI (idle high) Input sampled, pin should idle high
0 X X X Pins under port control (standard I/O port)