MC68HC908AS32A Datasheet, PDF (216/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Peripheral Interface (SPI)
To clear the MODF flag, read the SPSCR and then write to the SPCR register. This entire clearing
procedure must occur with no MODF condition existing or else the flag will not be cleared.
16.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests:
Table 16-2. SPI Interrupts
Flag
SPTE (transmitter empty)
SPRF (receiver full)
OVRF (overflow)
MODF (mode fault)
Request
SPI transmitter CPU interrupt request (SPTIE = 1)
SPI receiver CPU interrupt request (SPRIE = 1)
SPI receiver/error interrupt request (SPRIE = 1, ERRIE = 1)
SPI receiver/error interrupt request (SPRIE = 1, ERRIE = 1,
MODFEN = 1)
The SPI transmitter interrupt enable bit (SPTIE) enables the SPTE flag to generate transmitter CPU
interrupt requests.
The SPI receiver interrupt enable bit (SPRIE) enables the SPRF bit to generate receiver CPU interrupt,
provided that the SPI is enabled (SPE = 1).
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF flags to generate a
receiver/error CPU interrupt request.
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF
flag is enabled to generate receiver/error CPU interrupt requests.
SPTE SPTIE SPE
SPRIE SPRF
SPI TRANSMITTER
CPU INTERRUPT REQUEST
ERRIE
MODF
OVRF
SPI RECEIVER/ERROR
CPU INTERRUPT REQUEST
Figure 16-9. SPI Interrupt Request Generation
Two sources in the SPI status and control register can generate CPU interrupt requests:
1. SPI receiver full bit (SPRF) — The SPRF bit 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 can generate an SPI receiver/error CPU interrupt request.
2. SPI transmitter empty (SPTE) — The SPTE bit 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 can generate an SPTE CPU interrupt request.
MC68HC908AS32A Data Sheet, Rev. 2.0
216
Freescale Semiconductor