mc68hc908sr12 Freescale Semiconductor, Inc, mc68hc908sr12 Datasheet - Page 272

• Manufacturer Part Number: mc68hc908sr12
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Serial Communications Interface (SCI)
16.7 SCI During Break Module Interrupts
16.8 I/O Signals
16.8.1 TxD (Transmit Data)
Data Sheet
272
NOTE:
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
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 2-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.
Port B shares two of its pins with the SCI module.
The two SCI I/O pins are:
When the SCI is enabled (ENSCI=1), the PTB2/SDA1/TxD pin becomes
the serial data output, TxD, from the SCI transmitter regardless of the
state of the DDRB2 bit in data direction register B (DDRB). The TxD pin
is an open-drain output and requires a pullup resistor to be connected for
proper SCI operation.
The PTB2/SDA1/TxD pin is an open-drain pin when configured as an
output. Therefore, when configured as a general purpose output pin
(PTB2), a pullup resistor must be connected to this pin.
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PTB2/SDA1/TxD — Transmit data
PTB3/SCL1/RxD — Receive data
Serial Communications Interface (SCI)
MC68HC908SR12•MC68HC08SR12 — Rev. 5.0
Freescale Semiconductor