MC68HC908EY16 Datasheet, PDF (180/278 Pages) Motorola, Inc – Microcontrollers

Serial Peripheral Interface (SPI) Module
15.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests:
Table 15-3. 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.
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.
15.8 Queuing Transmission Data
The double-buffered transmit data register allows a data byte to be queued and transmitted. For an SPI
configured as a master, a queued data byte is transmitted immediately after the previous transmission
has completed. The SPI transmitter empty flag (SPTE in SPSCR) indicates when the transmit data buffer
is ready to accept new data. Write to the SPI data register only when the SPTE bit is high. Figure 15-10
shows the timing associated with doing back-to-back transmissions with the SPI (SPSCK has
CPHA:CPOL = 1:0).
For a slave, the transmit data buffer allows back-to-back transmissions to occur without the slave having
to time the write of its data between the transmissions. Also, if no new data is written to the data buffer,
the last value contained in the shift register will be the next data word transmitted.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
180
Freescale Semiconductor