RPAD
RMASK
Bit mask/pad
Bus (peripheral configuration bus or DMA bus)
32
RROT
32
Programmable rotate by:
0, 4, 8, 12, 16, 20, 24, 28
32
Bit reverse
RRVRS
32
Parallel read from
XRBUF[n]
RPBIT
1097
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
24.0.21.2 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 CPU (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.
This formatting unit consists of three stages:
•
Bit mask and pad (masks off bits, performs sign extension)
•
Rotate right (aligns data within word)
•
Bit reversal (selects between MSB first or LSB first)
shows a block diagram of the receive formatting unit, and
shows the transmit
formatting unit. Note that the order in which data flows through the three stages is different between the
transmit and receive formatting units.
Figure 24-19. Receive Format Unit