Registers
1456
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Serial Peripheral Interface (SPI)
29.3.13 SPI Transmit Data Register 1 (SPIDAT1)
The SPI transmit data register (SPIDAT1) is shown in
and described in
(1)
Not all devices support multiple slave chip select (SPIx_SCS[n]) pins, see your device-specific data manual for supported pins.
Figure 29-30. SPI Data Register 1 (SPIDAT1)
31
29
28
27
26
25
24
Reserved
CSHOLD
Reserved
WDEL
DFSEL
R-0
R/W-0
R-0
R/W-0
R/W-0
23
16
CSNR[
n
]
(1)
R/W-0
15
0
TXDATA
R/W-0
LEGEND: R/W = Read/Write; R = Read only; -
n
= value after reset
Table 29-21. SPI Data Register 1 (SPIDAT1) Field Descriptions
Bit
Field
Value
Description
31-29
Reserved
0
Reads return zero and writes have no effect.
28
CSHOLD
Chip select hold mode. The CSHOLD bit is supported in master mode only. In slave mode, this bit
is ignored. CSHOLD defines the behavior of the chip select line at the end of a data transfer.
0
The chip select signal is deactivated at the end of a transfer after the T2CDELAY time has passed.
1
The chip select signal is held active at the end of a transfer until a control field with new data and
control information is loaded into SPIDAT1. If the new chip select hold information equals the
previous one, the active chip select signal is extended until the end of transfer with CSHOLD
cleared.
27
Reserved
0
Reads return zero and writes have no effect.
26
WDEL
Enable the delay counter at the end of the current transaction. The WDEL bit is supported in
master mode only. In slave mode, this bit is ignored.
0
No delay will be inserted. However, SPIx_SCS[n] pin will still be deactivated for at least 2 SPI
module clock cycles if CSHOLD = 0.
1
After a transaction, SPIFMT
n
.WDELAY of the selected data format will be loaded into the delay
counter. No transaction will be performed until the SPIFMT
n
.WDELAY counter overflows. The
SPIx_SCS[n] pin will be deactivated for at least ( 2) × SPI module clock period.
25-24
DFSEL
0-3h
Data word format select
0
Data word format 0 is selected
1h
Data word format 1 is selected
2h
Data word format 2 is selected
3h
Data word format 3 is selected
Note: Preselecting a Format Register.
Writing to just the control field (using byte writes) does
not initiate any SPI transfer in master mode. This feature can be used to set up SPIx_CLK phase
or polarity before actually starting the transfer by just updating the DFSEL fields in the control field
to select the required phase/polarity combination.
23-16
CSNR[
n
]
Chip select number. The CSNR field defines the state of the SPIx_SCS[n] pins during a master
data transfer. The value of the CSNR field is driven directly on the SPIx_SCS[n] pins. Each bit in
the CSNR field corresponds to an SPIx_SCS[n] pin, for example, CSNR[0] corresponds to
SPIx_SCS[0] (see your device-specific data manual to determine how many SPI pins are available
on your device).
The state of the chip select pins when no transmissions are active is specified through the CSDEF
field in the SPI default chip select register (SPIDEF). The chip select pins can remain in their
active state by setting the CSHOLD bit to 1. When the SPI is configured in slave mode, this field
must be written as 00h.
0
SPIx_SCS[n] pin is driven low.
1
SPIx_SCS[n] pin is driven high.