For transmission using A-law compression, make sure the 13 data bits are left-justified in DXR1, with the
remaining three low-order bits filled with 0s as shown in
000
2-0
Value
15-3
A-law format in DXR1
Figure 15-55. A-Law Transmit Data Companding Format
15.8.11.3 Capability to Compand Internal Data
If the McBSP is otherwise unused (the serial port transmit and receive sections are reset), the companding
hardware can compand internal data.
15.8.11.4 Option to Transmit LSB First
Normally, the McBSP transmit or receives all data with the most significant bit (MSB) first. However, certain 8-bit
data protocols (that do not use companded data) require the least significant bit (LSB) to be transferred first. If
you set XCOMPAND = 01b in XCR2, the bit ordering of 8-bit words is reversed (LSB first) before being sent from
the serial port. Similar to companding, this feature is enabled only if the appropriate word length bits are set to 0,
indicating that 8-bit words are to be transferred serially. If either phase of the frame does not have an 8-bit word
length, the McBSP assumes the word length is eight bits and LSB-first ordering is done.
15.8.12 Set the Transmit Data Delay
Table 15-59. Register Bits Used to Set the Transmit Data Delay
Register
Bit
Name
Function
Type
Reset
Value
XCR2
1-0
XDATDLY
Transmitter data delay
R/W
00
XDATDLY = 00
0-bit data delay
XDATDLY = 01
1-bit data delay
XDATDLY = 10
2-bit data delay
XDATDLY = 11
Reserved
15.8.12.1 Data Delay
The start of a frame is defined by the first clock cycle in which frame synchronization is found to be active.
The beginning of actual data reception or transmission with respect to the start of the frame can be delayed if
necessary. This delay is called data delay.
XDATDLY specifies the data delay for transmission. The range of programmable data delay is zero to two bit-
clocks (XDATDLY = 00b-10b), as described in
. In this figure, the data transferred
is an 8-bit value with bits labeled B7, B6, B5, and so on. Typically a 1-bit delay is selected, because data often
follows a 1-cycle active frame-synchronization pulse.
B5
B6
B7
B4
B5
B6
B7
B3
B4
B5
B6
B7
Data delay 2
D(R/X)
Data delay 1
D(R/X)
Data delay 0
D(R/X)
FS(R/X)
CLK(R/X)
1-bit delay
Á
Á
Á
Á
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
0-bit delay
2-bit delay
Figure 15-56. Range of Programmable Data Delay
Multichannel Buffered Serial Port (McBSP)
946
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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