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XRSR
XRBUF
32
32
32
SRCTL
Serializer
Control
Pin
function
control
AXRn Pin
Transmit
format unit
Receive
format unit
Preliminary
Architecture
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10.2.7 General Architecture
10.2.7.1 Serializers
shows the block diagram of the serializer and its interface to other units within the McASP.
The serializers take care of shifting serial data in and out of the McASP. Each serializer consists of a
shift register (XRSR), a data buffer (XRBUF), a control register (SRCTL), and logic to support the data
alignment options of the McASP. For each serializer, there is a dedicated serial data pin (AXRn) and a
dedicated control register (SRCTL[n]). The control register allows the serializer to be configured as a
transmitter, receiver, or as inactive. When configured as a transmitter the serializer shifts out data to the
serial data pin AXRn. When configured as a receiver, the serializer shifts in data from the AXRn pin.
The serializer is clocked from the transmit/receive section clock (ACLKX/ACLKR) if configured to
transmit/receive respectively.
All serializers that are configured to transmit operate in lock-step. Similarly, all serializers that are
configured to receive also operate in lock-step. This means that at most there are two zones per
McASP, one for transmit and one for receive.
Figure 10-21. Individual Serializer and Connections Within McASP
For receive, data is shifted in through the AXRn pin to the shift register XRSR. Once the entire slot of
data is collected in the XRSR, the data is copied to the data buffer XRBUF. The data is now ready to
be read by the processor through the RBUF register, which is an alias of the XRBUF for receive. When
the processor reads from the RBUF, the McASP passes the data from RBUF through the receive
format unit and returns the formatted data to the processor.
For transmit, the processor services the McASP by writing data into the XBUF register, which is an
alias of the XRBUF for transmit. The data automatically passes through the transmit format unit before
actually reaching the XRBUF register in the serializer. The data is then copied from XRBUF to XRSR,
and shifted out from the AXRn synchronously to the serial clock.
In DIT mode, in addition to the data, the serializer shifts out other DIT-specific information accordingly
(preamble, user data, etc.).
The serializer configuration is controlled by SRCTL[n].
10.2.7.2 Format Unit
The McASP has two data formatting units, one for transmit and one for receive. These units
automatically remap the data bits within the transmitted and received words between a natural format
for the processor (such as a Q31 representation) and the required format for the external serial device
(such as "I2S format"). During the remapping process, the format unit also can mask off certain bits or
perform sign extension.
Since all transmitters share the same data formatting unit, the McASP only supports one transmit
format at a time. For example, the McASP will not transmit in "I2S format" on serializer 0, while
transmitting "Left Justified" on serializer 1. Likewise, the receiver section of the McASP only supports
one data format at a time, and this format applies to all receiving serializers. However, the McASP can
transmit in one format while receiving in a completely different format.
1036
Multichannel Audio Serial Port (McASP)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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