Multichannel Selection Operation
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11.6 Multichannel Selection Operation
Multiple channels can be independently selected for the transmitter and receiver
by configuring the McBSP with a single-phase frame. Each frame represents a
time-division multiplexed data stream. The number of elements per frame repre-
sented by (R/X)FRLEN1 denotes the number of channels available for selection.
Thus, to save memory and bus bandwidth, multichannel selection allows inde-
pendent enabling of particular elements for transmission and reception. Up to
32 elements in a bit stream of up to 128 elements can be enabled at any given
time.
If a receive element is not enabled:
-
RRDY is not set to 1 upon reception of the last bit of the element.
-
RBR is not copied to DRR upon reception of the last bit of the element. Thus,
RRDY is not set active. This feature also implies that no interrupts or synchro-
nization events are generated for this element.
If a transmit element is not enabled:
-
DX is in the high impedance state.
-
A DXR-to-XSR transfer is not automatically triggered at the end of serial
transmission of the related element.
-
XEMPTY and XRDY are not affected by the end of transmission of the re-
lated serial element.
An enabled transmit element can have its data masked or transmitted. When data
is masked, the DX pin is forced to the high-impedance state even though the
transmit channel is enabled.
11.6.1 Multichannel Operation Control Registers
The following control registers are used in multichannel operation:
-
The multichannel control register (MCR)
-
The transmit channel enable register (XCER)
-
The receive channel enable register (RCER)