Intel® PXA255 Processor Developer’s Manual 8-11
Synchronous Serial Port Controller

8.7.1.5 Serial Clock Rate (SCR)

The 8-bit serial clock rate (SCR) bit-field is used to sel ect the SSPC bit rate. The SSPC has 256 bit
rates, from 7.2Kbps to 1.8432 Mbps. The serial clock generator uses the internal 3.6864MHz
clock or an external clock provide d through SSPEXTCLK. The clock is divided by 2, then divided
by the programmable SCR value (0 to 255) plus 1 to generate the serial clock (SSPSCLK). The
resultant clock is driven on the SSPSCLK pin and is used by the SSP’s transmit logic to drive data
on the SSPTXD pin and to la tch dat a on the SSP RXD pi n. De pend ing on th e f ram e for m at se le cted ,
each transmitted bit is driven on either SSPSCLK’ s ris ing or falling edge and sampled on the
opposite clock edge.
This is a read/wri te register. Ignore reads fro m reserved bits. Write zeros to reserved bit s.
8.7.2 SSP Control Register 1 (SSCR1)
SSCR1, shown in Table 8-3, contains bit fields that control SSP functions.
Table 8-3. SSCR1 Bit Definitions (Sheet 1 of 2)
0x4100_0004 SSP Control Register 1 (SSCR1) Synchronous Serial Port Controller
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved RFT TFT
MWDS
SPH
SPO
LBM
TIE
RIE
Reset X0x0 0x0 0 0 0 0 0 0
Bits Name Description
0RIE Receive FIFO Interrupt Enable
0 = Receive FIFO interrupt is disabled
1 = Receive FIFO interrupt is enabled
1TIE
Transmit FIFO Interrupt Enable
0 = Transmit FIFO interrupt is disabled
1 = 1 - Transmit FIFO interrupt is enabled
2LBM
Loop-Back Mode
0 = Normal serial port operation enabled
1 = Output of transmit serial shifter internally connected to input of receive serial shifter
3 SPO Motorola SPI SSPSCLK polarity setting:
0 = The inactive or idle state of SSPSCLK is low.
1 = The inactive or idle state of SSPSCLK is high.
4 SPH
Motorola SPI SSPSCLK phase setting:
0 = SSPSCLK is inactive one cycle at the start of a frame and 1/2 cycle at the end of a
frame.
1 = SSPSCLK is inactive 1/2 cycle at the start of a frame and one cycle at the end of a
frame.
5MWDS
Microwire Transmit Data Size:
0 = 8-bit command words are transmitted.
1 = 16-bit command words are transmitted.