Transmitter Configuration
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SPRUI07–March 2020
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Multichannel Buffered Serial Port (McBSP)
12.9.10 Transmit Frame Length
Table 12-56. Register Bits Used to Set the Transmit Frame Length
Register Bit Name Function Type Reset Value
XCR1 14-8 XFRLEN1 Transmit frame length 1 R/W 000 0000
(XFRLEN1 + 1) is the number of serial words in phase 1 of the
transmit frame.
XFRLEN1 = 000 0000 1 word in phase 1
XFRLEN1 = 000 0001 2 words in phase 1
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XFRLEN1 = 111 1111 128 words in phase 1
XCR2 14-8 XFRLEN2 Transmit frame length 2 R/W 000 0000
If a dual-phase frame is selected, (XFRLEN2 + 1) is the
number of serial words in phase 2 of the transmit frame.
XFRLEN2 = 000 0000 1 word in phase 2
XFRLEN2 = 000 0001 2 words in phase 2
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XFRLEN2 = 111 1111 128 words in phase 2
12.9.10.1 Selected Frame Length
The transmit frame length is the number of serial words in the transmit frame. Each frame can have one or
two phases, depending on the value that you load into the XPHASE bit.
If a single-phase frame is selected (XPHASE = 0), the frame length is equal to the length of phase 1. If a
dual-phase frame is selected (XPHASE = 1), the frame length is the length of phase 1 plus the length of
phase 2.
The 7-bit XFRLEN fields allow up to 128 words per phase. See Table 12-57 for a summary of how to
calculate the frame length. This length corresponds to the number of words or logical time slots or
channels per frame-synchronization pulse.
NOTE: Program the XFRLEN fields with [w minus 1], where w represents the number of words per
phase. For example, if you want a phase length of 128 words in phase 1, load 127 into
XFRLEN1.
Table 12-57. How to Calculate Frame Length
XPHASE XFRLEN1 XFRLEN2 Frame Length
0 0 ≤ XFRLEN1 ≤ 127 Don't care (XFRLEN1 + 1) words
1 0 ≤ XFRLEN1 ≤ 127 0 ≤ XFRLEN2 ≤ 127 (XFRLEN1 + 1) + (XFRLEN2 + 1) words
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