Serial Communications Interface Module (SCI)
SCI During Break Module Interrupts
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Serial Communications Interface Module (SCI) 291
14.6 SCI During Break Module InterruptsThe system integration module (SIM) controls whether status bits in
other modules can be cleared during interrupts generated by the break
module. 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
logic 1 to the BCFE bit. If a status bit is cleared during the break sta te, 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), soft wa r e can r ead and write
I/O registers during the break state without affecting status bits. Some
status bits have a 2-step read/write clearing proce dure. If softw are does
the first step on such a bit before the break, the bit cannot change du ring
the break state as long as BCFE is at logic 0. After the break, doing the
second step clears the status bit.
14.7 I/O SignalsPort F shares two of its pins with the SCI module. The two SCI
input/output (I/O) pins are:
• PTF5/TxD — Transmit data
• PTF4/RxD — Receive data
14.7.1 PTF5/TxD (Transmit Data)
The PTF5/TxD pin is the serial data output from the SCI transmitter. The
SCI shares the PTF5/TxD pin with port E. When the SCI is enabled, the
PTF5/TxD pin is an output regardless of the state of the DDRF5 bit in
data direction register F (DDRF).