mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 930

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Functional Description
38.4.5.1 Transmit by DMA
Transmit by DMA is supported only when TXDMAE is set. A transmit DMA request is
asserted when both SPE and SPTEF are set. Then the on-chip DMA controller detects
this request and transfers data from memory into the SPI data register. After that, TX
DMA DONE is asserted to clear SPTEF automatically. This process repeats until all data
for transmission (the number is decided by the configuration register[s] of the DMA
controller) is sent.
When the FIFO feature is supported: In FIFO mode (FIFOMODE=1) and when a data
length of 8 bits is selected (SPIMODE=0), the DMA transfer for one transmit DMA
request can write more than 1 byte (up to 8 bytes) to the DL register because the TX
FIFO can store 8 bytes of transmit data. In FIFO mode (FIFOMODE=1) and when a data
length of 16 bits is selected (SPIMODE=1), the DMA transfer for one transmit DMA
request can write more than 1 word (up to 4 words) to the DH:DL registers because the
TX FIFO can store 4 words of transmit data. A larger number of bytes or words
transferred from memory to the SPI data register for each transmit DMA request results
in a lower total number of transmit DMA requests.
When the FIFO feature is supported and FIFOMODE is 0: After DMA transfers the first
byte to the SPI data register, the SPI pushes this data into the shifter, thereby making
SPTEF high again. This generates another DMA request immediately, but the CPU lacks
enough time to service the first DMA interrupt service request (ISR). The subsequent
DMA request is paced at the SPI transfer rate. Manage this behavior during the first byte
transfer through the DMA channel. Write the first byte to the SPI data register via the
CPU. The other bytes are transmitted by the DMA.
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
930
Freescale Semiconductor, Inc.