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SSInClk
SSInFss
SSInRx
SSInTx
Q
Q
Q
LSB
LSB
4 to 16 bits
MSB
MSB
SSInClk
SSInFss
SSInRx
LSB
SSInTx
MSB
LSB
LSB
MSB
MSB
MSB
LSB
4 to16 bits
Functional Description
1531
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Quad Synchronous Serial Interface (QSSI)
Figure 23-5. Freescale SPI Format (Continuous Transfer) with SPO = 0 and SPH = 0
In this configuration, during idle periods:
•
SSInClk is forced low
•
SSInFss is forced high
•
The transmit data line SSInDAT0 and SSInTX is in a tristate condition
•
When the QSSI is configured as a master, it enables the SSInClk pad
•
When the QSSI is configured as a slave, it disables the SSInClk pad
If the QSSI is enabled and valid data is in the transmit FIFO, the start of transmission is signified by the
SSInFss master signal being driven low, causing slave data to be enabled onto the SSInDAT1 and
SSInRX input line of the master. The master SSInDAT0 and SSInTX output pad is enabled.
One half SSInClk period later, valid master data is transferred to the SSInDAT0 and SSInTX pin. Once
both the master and slave data have been set, the SSInClk master clock pin goes High after one
additional half SSInClk period.
The data is now captured on the rising and propagated on the falling edges of the SSInClk signal.
In the case of a single word transmission, after all bits of the data word have been transferred, the
SSInFss line is returned to its idle High state one SSInClk period after the last bit has been captured.
However, in the case of continuous back-to-back transmissions, the SSInFss signal must be pulsed High
between each data word transfer because the slave select pin freezes the data in its serial peripheral
register and does not allow it to be altered if the SPH bit is clear. Therefore, the master device must raise
the SSInFss pin of the slave device between each data transfer to enable the serial peripheral data write.
On completion of the continuous transfer, the SSInFss pin is returned to its idle state one SSInClk period
after the last bit has been captured.
23.3.7.4 Freescale SPI Frame Format with SPO = 0 and SPH = 1
The transfer signal sequence for Freescale SPI format with SPO = 0 and SPH = 1 is shown in
, which covers both single and continuous transfers.
NOTE:
This Freescale SPI frame format configuration is only available when operating in legacy SSI
mode of operation.
NOTE: Q is undefined.
Figure 23-6. Freescale SPI Frame Format with SPO = 0 and SPH = 1
In this configuration, during idle periods: