MC68HC908AS32A Datasheet, PDF (177/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

SCI During Break Module Interrupts
If SCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
14.5.2 Stop Mode
The SCI module is inactive after the execution of a STOP instruction. The STOP instruction does not
affect SCI register states. SCI module operation resumes after an external interrupt.
Because the internal clock is inactive during stop mode, entering stop mode during an SCI transmission
or reception results in invalid data.
14.6 SCI During Break Module Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state.
To allow software to clear status bits during a break interrupt, write a 1 to the BCFE bit. If a status bit is
cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default state),
software can read and write I/O registers during the break state without affecting status bits. Some status
bits have a two-step read/write clearing procedure. If software does the first step on such a bit before the
break, the bit cannot change during the break state as long as BCFE is at 0. After the break, doing the
second step clears the status bit.
14.7 I/O Signals
Port E shares two of its pins with the SCI module. The two SCI I/O pins are:
• PTE0/TxD — Transmit data
• PTE1/RxD — Receive data
14.7.1 PTE0/SCTxD (Transmit Data)
The PTE0/TxD pin is the serial data output from the SCI transmitter. The SCI shares the PTE0/TxD pin
with port E. When the SCI is enabled, the PTE0/TxD pin is an output regardless of the state of the DDRE2
bit in data direction register E (DDRE).
14.7.2 PTE1/SCRxD (Receive Data)
The PTE1/RxD pin is the serial data input to the SCI receiver. The SCI shares the PTE1/RxD pin with port
E. When the SCI is enabled, the PTE1/RxD pin is an input regardless of the state of the DDRE1 bit in data
direction register E (DDRE).
MC68HC908AS32A Data Sheet, Rev. 2.0
Freescale Semiconductor
177