For 2-bit delay:
Next frame-synchronization
pulse here or later is OK.
For 1-bit delay:
Next frame-synchronization
pulse here or later is OK.
For 0-bit delay:
Next frame-synchronization
pulse here or later is OK.
CLKR/CLKX
FSR/FSX
DR/DX
Last bit of
current frame
Earliest possible
time to begin transfer
of next frame
Figure 15-25. Proper Positioning of Frame-Synchronization Pulses
15.4.4 Overwrite in the Transmitter
As described in McBSP transmission (
), the transmitter must copy the data previously written to
the DXRs by the CPU or DMA controller into the XSRs and then shift each bit from the XSRs to the DX pin. If
new data is written to the DXRs before the previous data is copied to the XSRs, the previous data in the DXRs is
overwritten and thus lost.
15.4.4.1 Example of Overwrite Condition
shows what happens if the data in DXR1 is overwritten before being transmitted. Initially, DXR1 is
loaded with data C. A subsequent write to DXR1 overwrites C with D before C is copied to XSR1. Thus, C is
never transmitted on DX.
Write to DXR1(D)
Á
Á
Á
Á
Á
Á
Á
Á
Write to DXR1(E)
DXR1 to XSR1 Copy(D)
Write to DXR1(C)
D5
D6
D7
B0
B1
B2
B3
B4
B5
B6
B7
A0
A1
XRDY
DX
FSX
CLKX
Á
Á
Á
Á
Á
Á
Á
Á
Figure 15-26. Data in the McBSP Transmitter Overwritten and Thus Not Transmitted
15.4.4.2 Preventing Overwrites
You can prevent CPU overwrites by making the CPU:
• Poll for XRDY = 1 in SPCR2 before writing to the DXR(s). XRDY is set when data is copied from DXR1 to
XSR1 and is cleared when new data is written to DXR1.
Multichannel Buffered Serial Port (McBSP)
900
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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