MC908AZ32ACFUE Datasheet, PDF (153/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Low-Power Modes
• Parity error (PE) — The PE bit in SCS1 is set when the SCI detects a parity error in incoming data.
The parity error interrupt enable bit, PEIE, in SCC3 enables PE to generate SCI error CPU interrupt
requests.
16.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
16.5.1 Wait Mode
The SCI module remains active in wait mode. Any enabled CPU interrupt request from the SCI module
can bring the MCU out of wait mode.
If SCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
16.5.2 Stop Mode
The SCI module is inactive in stop mode. The STOP instruction does not affect SCI register states. Any
enabled CPU interrupt request from the SCI module does not bring the MCU out of Stop mode. SCI
module operation resumes after the MCU exits stop mode.
Because the internal clock is inactive during stop mode, entering stop mode during an SCI transmission
or reception results in invalid data.
16.6 SCI During Break Module Interrupts
The BCFE bit in the break flag control register (BFCR) enables software to clear status bits during the
break state. (See Chapter 11 Brake Module).
To allow software to clear status bits during a break interrupt, write a logic 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 logic 0 to the BCFE bit. With BCFE at logic 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 logic 0. After the
break, doing the second step clears the status bit.
16.7 I/O Signals
Port E shares two of its pins with the SCI module. The two SCI I/O pins are:
• PTE0/SCTxD — Transmit data
• PTE1/SCRxD — Receive data
16.7.1 PTE0/SCTxD (Transmit Data)
The PTE0/SCTxD pin is the serial data output from the SCI transmitter. The SCI shares the PTE0/SCTxD
pin with port E. When the SCI is enabled, the PTE0/SCTxD pin is an output regardless of the state of the
DDRE2 bit in data direction register E (DDRE).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
153