![Texas Instruments AM1808 Technical Reference Manual Download Page 1226](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_10945581226.webp)
Architecture
1226
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.9 Multichannel Selection Modes
This section defines and provides the functions and all related information concerning the multichannel
selection modes.
25.2.9.1 Channels, Blocks, and Partitions
A McBSP channel is a time slot for shifting in/out the bits of one serial word. Each McBSP supports up to
128 channels for reception and 128 channels for transmission. In the receiver and in the transmitter, the
128 available channels are divided into eight blocks that each contain 16 contiguous channels:
Block 0: Channels 0 through 15
Block 4: Channels 64 through 79
Block 1: Channels 16 through 31
Block 5: Channels 80 through 95
Block 2: Channels 32 through 47
Block 6: Channels 96 through 111
Block 3: Channels 48 through 63
Block 7: Channels 112 through 127
The blocks are assigned to partitions according to the selected partition mode. In the 2-partition mode, you
assign one even-numbered block (0, 2, 4, or 6) to partition A and one odd-numbered block (1, 3, 5, or 7)
to partition B. In the 8-partition mode, blocks 0 through 7 are automatically assigned to partitions, A
through H, respectively.
The number of partitions for reception and the number of partitions for transmission are independent. For
example, it is possible to use 2 receive partitions (A and B) and 8 transmit partitions (A through H).
25.2.9.2 Multichannel Selection
When McBSP uses a time-division multiplexed (TDM) data stream while communicating with other
McBSPs or serial devices, the McBSP may need to receive and/or transmit on only a few channels. To
save memory and bus bandwidth, you can use a multichannel selection mode to prevent data flow in
some of the channels. The McBSP has one receive multichannel selection mode and three transmit
multichannel selection modes.
Each channel partition has a dedicated channel enable register. If the appropriate multichannel selection
mode is on, each bit in the register controls whether data flow is allowed or prevented in one of the
channels that is assigned to that partition.
25.2.9.3 Configuring a Frame for Multichannel Selection
Before you enable a multichannel selection mode, make sure you properly configure the data frame:
•
Select a single-phase frame (RPHASE/XPHASE = 0). Each frame represents a TDM data stream.
•
Set a frame length (RFRLEN1/XFRLEN1) that includes the highest-numbered channel that is to be
used. For example, if you plan to use channels 0, 15, and 39 for reception, the receive frame length
must be at least 40 (RFRLEN1 = 39). If XFRLEN1 = 39 in this case, the receiver creates 40 time slots
per frame but only receives data during time slots 0, 15, and 39 of each frame.
NOTE:
The frame-sync pulse can be generated internally by the sample rate generator or it can be
supplied externally by another source. In a multichannel mode configuration with external
frame-sync generation, the McBSP transmitter will ignore the first frame-sync pulse after it is
taken out of reset. The transmitter will transmit only on the second frame-sync pulse. The
receiver will shift in data on the first frame-sync pulse, regardless of whether it is generated
internally or externally.