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D(R/X)
FS(R/X)
C5
C6
C7
B0
B2
B3
B4
B5
B6
B7
A0
A1
B1
CLK(R/X)
Architecture
1210
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.5.5.7 32-Bit Bit Reversal: RWDREVRS, XWDREVRS
Normally all transfers are sent and received with the MSB first; however, you can reverse the
receive/transmit bit ordering of a 32-bit element (LSB first) using the 32-bit reversal feature of the McBSP
by setting all of the following:
•
(R/X)WDREVRS = 1 in the receive/transmit control register (RCR/XCR).
•
(R/X)COMPAND = 01b in RCR/XCR.
•
(R/X)WDLEN(1/2) = 101b in RCR/XCR to indicate 32-bit elements.
When you set the register fields as above, the bit ordering of the 32-bit element is reversed before being
received by or sent from the serial port. If the (R/W)WDREVRS and (R/X)COMPAND fields are set as
above, but the element size is not set to 32-bit, operation is undefined.
25.2.6 McBSP Buffer FIFO (BFIFO)
The McBSP Buffer FIFO (BFIFO) provides additional data buffering for the McBSP. The time it takes the
host CPU or DMA controller to respond to DMA requests from the McBSP may vary; the additional
buffering provided by the BFIFO allows greater tolerance to such variations. For convenience, the BFIFO
is treated here as a block between the McBSP and the host/DMA controller (see
). Details on
configuration of the BFIFO are provided in
.
25.2.7 McBSP Standard Operation
During a serial transfer, there are typically periods of serial port inactivity between packets or transfers.
The receive and transmit frame synchronization pulse occurs for every serial transfer. When the McBSP is
not in the reset state and has been configured for the desired operation, a serial transfer can be initiated
by programming (R/X)PHASE = 0 for a single-phase frame with the required number of elements
programmed in (R/X)FRLEN1. The number of elements can range from 1 to 128 ((R/X)FRLEN1 = 00h to
7Fh). The required serial element length is set in the (R/X)WDLEN1 field in the (R/X)CR. If a dual-phase
frame is required for the transfer, RPHASE = 1 and each (R/X)FRLEN1/2 can be set to any value between
0h and 7Fh.
shows a single-phase data frame of one 8-bit element. Since the transfer is configured for a
1-bit data delay, the data on the DX and DR pins are available one bit clock after FS(R/X) goes active.
This figure, as well as all others in this section, use the following assumptions:
•
(R/X)PHASE = 0, specifying a single-phase frame
•
(R/X)FRLEN1 = 0b, specifying one element per frame
•
(R/X)WDLEN1 = 000b, specifying eight bits per element
•
(R/X)FRLEN2 = (R/X)WDLEN2 = Value is ignored
•
CLK(R/X)P = 0, specifying that the receive data is clocked on the falling edge and that transmit data is
clocked on the rising edge
•
FS(R/X)P = 0, specifying that active (high) frame sync signals are used
•
(R/X)DATDLY = 01b, specifying a 1-bit data delay
Figure 25-15. McBSP Standard Operation