Control Registers
1181
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Multi-Buffered Serial Peripheral Interface Module (MibSPI) with Parallel Pin
Option (MibSPIP)
Table 24-29. SPI Data Format Registers (SPIFMT) Field Descriptions (continued)
Bit
Field
Value
Description
19
HDUPLEX_ENAx
Half Duplex transfer mode enable for Data Format x. This bit controls the I/O function of
SOMI/SIMO lines for a specific requirement where in the case of Master mode, TX pin -
SIMO will act as an RX pin, and in the case of Slave mode, RX pin - SIMO will act as a
TX pin.
0
Normal Full Duplex transfer.
1
If MASTER = 1, SPISIMO pin will act as an RX pin (No TX possible) If MASTER = 0,
SPISIMO pin will act as a TX pin (No RX possible).
For all normal operations, HDUPLEX_ENAx bits should always remain 0. It is intended for
the usage when the SPISIMO pin is used for both TX and RX operations at different
times.
18
DIS CS TIMERS
Disable chip-select timers for this format. The C2TDELAY and T2CDELAY timers are by
default enabled for all the data format registers. Using this bit, these timers can be
disabled for a particular data format, if they are not required. When a master is handling
multiple slaves, with varied set-up hold requirement, the application can selectively
choose to include or not include the chip-select delay timers for any slaves.
0
Both C2TDELAY and T2CDELAY counts are inserted for the chip selects.
1
No C2TDELAY or T2CDELAY is inserted in the chip select timings.
17
POLARITY
SPI data format x clock polarity. POLARITYx defines the clock polarity of data format x.
The following restrictions apply when switching clock phase and/or polarity:
• In 3-pin/4-pin with SPIENA pin configuration of a slave SPI, the clock phase and
polarity cannot be changed on-the-fly between two transfers. The slave should be reset
and reconfigured if clock phase/polarity needs to be switched. In summary, SPI format
switching is not fully supported in slave mode.
• Even while using chip select pins, the polarity of SPICLK can be switched only while
the slave is not selected by a valid chip select. The master SPI should ensure that
while switching SPICLK polarity, it has deselected all of its slaves. Otherwise, the
switching of SPICLK polarity may be incorrectly treated as a clock edge by some
slaves.
0
If POLARITYx is cleared to 0, the SPI clock signal is low-inactive, that is, before and after
data transfer the clock signal is low.
1
If POLARITYx is set to 1, the SPI clock signal is high-inactive, that is, before and after
data transfer the clock signal is high.
16
PHASE
SPI data format x clock delay. PHASEx defines the clock delay of data format x.
0
If PHASEx is cleared to 0, the SPI clock signal is not delayed versus the transmit/receive
data stream. The first data bit is transmitted with the first clock edge and the first bit is
received with the second (inverse) clock edge.
1
If PHASEx is set to 1, the SPI clock signal is delayed by a half SPI clock cycle versus the
transmit/receive data stream. The first transmit bit has to output prior to the first clock
edge. The master and slave receive the first bit with the first edge.
15-8
PRESCALE
SPI data format x prescaler. PRESCALEx determines the bit transfer rate of data format x
if the SPI is the network master. PRESCALEx is use to derive SPICLK from VCLK. If the
SPI is configured as slave, PRESCALEx
does not need
to be configured. The clock rate
for data format x can be calculated as:
BR
Formatx
= VCLK / (PRE 1)
Note: When PRESCALEx is cleared to 0, the SPI clock rate defaults to VCLK/2.
7-5
Reserved
0
Reads return 0. Writes have no effect.
4-0
CHARLEN
0-1Fh
SPI data format x data-word length. CHARLENx defines the word length of data format x.
Legal values are 0x02 (data word length = 2 bit) to 10h (data word length = 16). Illegal
values, such as 00 or 1Fh are not allowed; their effect is indeterminate.