MC908QY8CDWE Datasheet, PDF (170/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Serial Peripheral Interface (SPI) Module
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF bits to generate a receiver/error
interrupt request.
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF
bit is enabled by the ERRIE bit to generate receiver/error interrupt requests.
The following sources in the SPI status and control register can generate interrupt requests:
• SPI receiver full bit (SPRF) — SPRF becomes set every time a byte transfers from the shift register
to the receive data register. If the SPI receiver interrupt enable bit, SPRIE, is also set, SPRF
generates an SPI receiver/error interrupt request.
• SPI transmitter empty bit (SPTE) — SPTE becomes set every time a byte transfers from the
transmit data register to the shift register. If the SPI transmit interrupt enable bit, SPTIE, is also set,
SPTE generates an SPTE interrupt request.
15.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
15.5.1 Wait Mode
The SPI module remains active after the execution of a WAIT instruction. In wait mode the SPI module
registers are not accessible by the CPU. Any enabled interrupt request from the SPI module can bring the
MCU out of wait mode.
If SPI module functions are not required during wait mode, reduce power consumption by disabling the
SPI module before executing the WAIT instruction.
To exit wait mode when an overflow condition occurs, enable the OVRF bit to generate interrupt requests
by setting the error interrupt enable bit (ERRIE). See 15.4 Interrupts.
15.5.2 Stop Mode
The SPI module is inactive after the execution of a STOP instruction. The STOP instruction does not
affect register conditions. SPI operation resumes after an external interrupt. If stop mode is exited by
reset, any transfer in progress is aborted, and the SPI is reset.
15.6 SPI During Break 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 break flag control register (BFCR) enables software to clear status
bits during the break state. See BFCR in the SIM section of this data sheet.
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. 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 BCFE. With BCFE cleared (its default state),
software can read and write 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 cleared. After the break, doing the
second step clears the status bit.
MC68HC908QB8 Data Sheet, Rev. 3
168
Freescale Semiconductor