Multi-Buffer RAM
1216
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Multi-Buffered Serial Peripheral Interface Module (MibSPI) with Parallel Pin
Option (MibSPIP)
24.10.3 Multi-Buffer RAM Transmit Data Register (TXRAM)
Each word of TXRAM is a transmit-buffer register.
NOTE:
Writing to only the control fields, bits 28 through 16, does not initiate any SPI transfer in
master mode. This feature can be used to set up SPICLK phase or polarity before actually
starting the transfer by only updating the DFSEL bit field to select the required phase and
polarity combination.
Figure 24-77. Multi-Buffer RAM Transmit Data Register (TXRAM)
[offset = RAM Base + 0h-1FFh]
31
29
28
27
26
25
24
23
16
BUFMODE
CSHOLD
LOCK
WDEL
DFSEL
CSNR
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
15
0
TXDATA
R/W-0
LEGEND: R/W = Read/Write; -
n
= value after reset
Table 24-55. Multi-Buffer RAM Transmit Data Register (TXRAM) Field Descriptions
Bit
Field
Value
Description
31-29
BUFMODE
Specify conditions that are recognized by the sequencer to initiate transfers of each buffer word.
When one of the "skip" modes is selected, the sequencer checks the buffer status every time it
reads from this buffer. If the current buffer status (TXFULL, RXEMPTY) does not match, the buffer
is skipped without a data transfer.
When one of the "suspend" modes is selected, the sequencer checks the buffer status when it
reads from this buffer. If TXFULL and/or RXEMPTY do not match, the sequencer waits until a
match occurs. No data transfer is initiated until the status condition of this buffer changes.
0
disabled.
The buffer is disabled.
1h
skip single-transfer mode.
Skip this buffer until the corresponding TXFULL flag is set (new
transmit data is available).
2h
skip overwrite-protect mode.
Skip this buffer until the corresponding RXEMPTY flag is set (new
receive data can be stored in RXDATA without data loss).
3h
skip single-transfer overwrite-protect mode
. Skip this buffer until both of the corresponding
TXFULL and RXEMPTY flags are set. (new transmit data available and previous data received by
the host).
4h
continuous mode.
Initiate a transfer each time the sequencer checks this buffer. Data words are
retransmitted if the buffer has not been updated. Receive data is overwritten, even if it has not
been read.
5h
suspend single-transfer mode.
Suspend-to-wait until the corresponding TXFULL flag is set (the
sequencer stops at the current buffer until new transmit data is written in the TXDATA field).
6h
suspend overwrite-protect mode.
Suspend-to-wait until the corresponding RXEMPTY flag is set
(the sequencer stops at the current buffer until the previously-received data is read by the host.
7h
suspend single-transfer overwrite-protect mode.
Suspend-to-wait until the corresponding
TXFULL and RXEMPTY flags are set (the sequencer stops at the current buffer until new transmit
data is written into the TXDATA field and the previously-received data is read by the host).
28
CSHOLD
Chip select hold mode. The CSHOLD bit is supported in master mode only, it is ignored in slave
mode. 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.
If two consecutive transfers are dedicated to the same chip select this chip select signal will be
deactivated for at least 2VCLK cycles before it is activated again.
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 number equals the previous one,
the active chip select signal is extended until the end of transfer with CSHOLD cleared, or until the
chip-select number changes.