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SSInClk
SSInFss
MSB
LSB
4 to 16 bits
SSInTx/SSInRx
Functional Description
1529
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Quad Synchronous Serial Interface (QSSI)
For both formats, the serial clock (SSInClk) is held inactive while the QSSI is idle, and SSInClk transitions
at the programmed frequency only during active transmission or reception of data. The idle state of
SSInClk is utilized to provide a receive timeout indication that occurs when the receive FIFO still contains
data after a timeout period.
For Freescale SPI frame format, the serial frame (SSInFss) pin is active low, and is asserted (pulled
down) during the entire transmission of the frame.
For TI synchronous serial frame format, the SSInFss pin is pulsed for one serial clock period starting at its
rising edge, prior to the transmission of each frame. For this frame format, both the QSSI and the off-chip
slave device drive their output data on the rising edge of SSInClk and latch data from the other device on
the falling edge.
is a synopsis of the features supported in each frame format when operating in legacy Mode:
Table 23-3. Legacy Mode TI, Freescale SPI Frame Format Features
Feature
TI Mode
Freescale SPI Mode
Frame hold
Not available
Available
High speed (master RX only)
Not available
Available
SPO and SPH configuration
Not available
Available and can be used in combination
with frame hold and high-speed mode
Frequency (system clock: SSInCLK)
Master 1:2
Slave 1:12
Master 1:2
Slave 1:12
For advanced, bi-, and quad-SSI modes using the Freescale SPI format or the bi- and quad-SSI modes
using the TI format, the following features are supported:
•
Frame hold
•
High speed (master RX only)
•
SPO and SPH configuration with SPO = 0 and SPH = 0 only allowed
•
Frequency (system clock: SSInCLK):
–
Master 1:2
–
Slave 1:12
23.3.7.1 TI Synchronous Serial Frame Format
shows the TI synchronous serial frame format for a single transmitted frame.
Figure 23-2. TI Synchronous Serial Frame Format (Single Transfer)
In this mode, SSInClk and SSInFss are forced Low, and the transmit data line SSInDAT0/SSInTX is in a
tristate condition whenever the QSSI is idle. Once the bottom entry of the transmit FIFO contains data,
SSInFss is pulsed High for one SSInClk period. The value to be transmitted is also transferred from the
transmit FIFO to the serial shift register of the transmit logic. On the next rising edge of SSInClk, the MSB
of the 4- to 16-bit data frame is shifted out on the SSInDAT0 and SSInTX pins. Likewise, the MSB of the
received data is shifted onto the SSInDAT1 and SSInRX pins by the off-chip serial slave device.
Both the QSSI and the off-chip serial slave device then clock each data bit into their serial shifter on each
falling edge of SSInClk. The received data is transferred from the serial shifter to the receive FIFO on the
first rising edge of SSInClk after the LSB has been latched.
shows the TI synchronous serial frame format when back-to-back frames are transmitted.