15.6.4 Clock Stop Mode Timing Diagrams
The timing diagrams for the four possible clock stop mode configurations are shown here. Notice that the frame-
synchronization signal used in clock stop mode is active throughout the entire transmission as a slave-enable
signal. Although the timing diagrams show 8-bit transfers, the packet length can be set to 8, 12, 16, 20, 24, or
32 bits per packet. The receive packet length is selected with the RWDLEN1 bits of RCR1, and the transmit
packet length is selected with the XWDLEN1 bits of XCR1. For clock stop mode, the values of RWDLEN1 and
XWDLEN1 must be the same because the McBSP transmit and receive circuits are synchronized to a single
clock.
Note
Even if multiple words are consecutively transferred, the CLKX signal is always stopped and the FSX
signal returns to the inactive state after a packet transfer. When consecutive packet transfers are
performed, this leads to a minimum idle time of two bit-periods between each packet transfer.
B1
B2
B4
B3
B0
B5
B6
B7
B0
B1
B2
B3
B4
B5
B6
B7
FSX/SPISTE
DX or DR/SIMO
(from master)
CLKX/SPICLK
DX or DR/SOMI
(from slave)
A.
If the McBSP is the SPI master (CLKXM = 1), SIMO = DX. If the McBSP is the SPI slave (CLKXM = 0), SIMO = DR.
B.
If the McBSP is the SPI master (CLKXM = 1), SOMI = DR. If the McBSP is the SPI slave (CLKXM = 0), SOMI = DX.
Figure 15-37. SPI Transfer With CLKSTP = 10b (No Clock Delay), CLKXP = 0, and CLKRP = 0
B1
B2
B4
B3
B0
B5
B6
B7
B0
B1
B2
B3
B4
B5
B6
B7
FSX/SPISTE
DX or DR/SIMO
(from master)
CLKX/SPICLK
DX or DR/SOMI
(from slave)
A.
If the McBSP is the SPI master (CLKXM = 1), SIMO = DX. If the McBSP is the SPI slave (CLKXM = 0), SIMO = DR.
B.
If the McBSP is the SPI master (CLKXM = 1), SOMI = DR. If the McBSP is the SPI slave (CLKXM = 0), SOMI = DX.
Figure 15-38. SPI Transfer With CLKSTP = 11b (Clock Delay), CLKXP = 0, CLKRP = 1
Multichannel Buffered Serial Port (McBSP)
914
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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