Intel PXA255 - Manual (Page 322)

8-14 Intel® PXA255 Processor Developer’s Manual
Synchronous Serial Port Controller
8.7.2.6 Microwire Transmit Data Size (MWDS)
The Microwire Transmit Data Size (MWDS) bit is used to select the 8- or 16-bit size for command
word transmissions in the National Microwire frame format. When the MWDS is set to “0”, 8-bit
command words are transmitted. When the MWDS is set to “1”, 16-bit command words are
transmitted. The MWDS setting is ignored for all other frame formats.
8.7.2.7 Transmit FIFO Interrupt/DMA Threshold (TFT)
This 4-bit value sets the level at or below which the FIFO controller triggers a DMA service
request and, if enabled, an interrupt request. Refer to
Table 8-4 for suggested TFT values
associated with DMA servicing.
8.7.2.8 Receive FIFO Interrupt/DMA Threshold (RFT)
This 4-bit value sets the level at or above which the FIFO controller triggers a DMA service
interrupt and, if enabled, an interrupt request. Refer to
Table 8-4 for suggested RFT values
associated with DMA servicing.
Be careful not to set the RFT value too high for your system or the FIFO could overrun because of
the bus latencies caused by other internal and external peripherals. This is especially the case for
interrupt and polled modes that require a longer time to service.
SSPRXD Bit<N>
Bit<N-
1>
... Bit<1> Bit<0>
MSB 4 to 16 Bits LSB
SPH = 0
SSPSCLK SPO=0
...
SSPSCLK SPO=1
...
SSPSFRM
...
SSPTXD Bit<N>
Bit<N-
1>
... Bit<1> Bit<0>
SSPRXD Bit<N>
Bit<N-
1>
... Bit<1> Bit<0>
MSB 4 to 16 Bits LSB
SPH = 1
Figure 8-4. Motorola SPI* Frame Formats for SPO and SPH Programming