The McBSP can also provide a slave-enable signal (SPISTE) on the FSX pin. If a slave-enable signal is
required, the FSX pin must be configured as an output and the transmitter must be configured so that a
frame-synchronization pulse is generated automatically each time a packet is transmitted (FSGM = 0). The
polarity of the FSX pin is programmable high or low; however, in most cases the pin must be configured active
low.
When the McBSP is configured as described for SPI-master operation, the bit fields for frame-synchronization
pulse width (FWID) and frame-synchronization period (FPER) are overridden, and custom frame-synchronization
waveforms are not allowed. To see the resulting waveform produced on the FSX pin, see the timing diagrams in
. The signal becomes active before the first bit of a packet transfer, and remains active until the
last bit of the packet is transferred. After the packet transfer is complete, the FSX signal returns to the inactive
state.
15.6.7 McBSP as an SPI Slave
An SPI interface with the McBSP used as a slave is shown in
. When the McBSP is configured as a
slave, DX is used as the SOMI signal and DR is used as the SIMO signal.
The register bit values required to configure the McBSP as a slave are listed in
are more details about configuration requirements.
McBSP slave
CLKX
DX
DR
FSX
SPI-compliant
master
SPICLK
SPISOMI
SPISIMO
SPISTE
Figure 15-42. SPI Interface With McBSP Used as Slave
Table 15-17. Bit Values Required to Configure the McBSP as an SPI Slave
Required Bit Setting
Description
CLKSTP = 10b or 11b
The clock stop mode (without or with a clock delay) is selected.
CLKXP = 0 or 1
The polarity of CLKX as seen on the MCLKX pin is positive (CLKXP = 0) or negative (CLKXP = 1).
CLKRP = 0 or 1
The polarity of MCLKR as seen on the MCLKR pin is positive (CLKRP = 0) or negative (CLKRP = 1).
CLKXM = 0
The MCLKX pin is an input pin, so that it can be driven by the SPI master. Because CLKSTP = 10b or
11b, MCLKR is driven internally by CLKX.
SCLKME = 0
The clock generated by the sample rate generator (CLKG) is derived from the CPU clock. (The
sample rate generator is used to synchronize the McBSP logic with the externally-generated master
clock.)
CLKSM = 1
CLKGDV = 1
The sample rate generator divides the CPU clock before generating CLKG.
FSXM = 0
The FSX pin is an input pin, so that it can be driven by the SPI master.
FSXP = 1
The FSX pin is active low.
XDATDLY = 00b
These bits must be 0s for SPI slave operation.
RDATDLY = 00b
When the McBSP is used as an SPI slave, the master clock and slave-enable signals are generated externally
by a master device. Accordingly, the CLKX and FSX pins must be configured as inputs. The MCLKX pin is
Multichannel Buffered Serial Port (McBSP)
918
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
Страница 2: ......