B5
B6
B7
B4
B5
B6
B7
B3
B4
B5
B6
B7
D(R/X)
data delay 2
data delay 1
D(R/X)
data delay 0
D(R/X)
FS(R/X)
CLK(R/X)
0-bit period
2-bit period
1-bit period
B7
B6
B5
2 Bit Periods
Framing Bit
CLKR
FSR
DR
Preliminary
www.ti.com
Architecture
Figure 11-30. Range of Programmable Data Delay
0-bit data delay:
Normally, a frame–synchronization pulse is detected or sampled with respect to an edge of internal
serial clock CLK(R/X). Thus, on the following cycle or later (depending on the data delay value), data
may be received or transmitted. However, in the case of 0–bit data delay, the data must be ready for
reception and/or transmission on the same serial clock cycle.
For reception, this problem is solved because receive data is sampled on the first falling edge of CLKR
where an active–high internal FSR is detected. However, data transmission must begin on the rising
edge of the internal CLKX clock that generated the frame synchronization. Therefore, the first data bit is
assumed to be present in XSR1, and thus on McBSP.DX. The transmitter then asynchronously detects
the frame–synchronization signal (FSX) going active high and immediately starts driving the first bit to
be transmitted on the McBSP.DX pin.
Figure 11-31. 2-Bit Data Delay Used to Skip a Framing Bit
11.2.8.6.11 Set the Transmit DXENA Mode
DXENA bit (SPRC1_REG[7]) is used to set the transmit DXENA (DX delay enable) mode.
The DXENA bit controls the delay enabler on the McBSP.DX pin. Set DXENA to enable an extra delay
for turn–on time. This bit does not control the data itself, so only the first bit is delayed (the delay is
given by a combinatorial delay buffer). The inserted delay: 7 ns, 14 ns (default), 20 ns or 28 ns can be
set using the DXENDLY bit field in XCCR_REG register. If you tie together the McBSP.DX pins of
multiple McBSPs, make sure DXENA = 1 to avoid having more than one McBSP transmitting on the
data line at one time.
11.2.8.6.12 Set the Transmit Interrupt Mode (legacy only)
The XINTM bit field (SPCRX_REG[5:4]) determines which event generates a transmit interrupt request
to the CPU.
1169
SPRUGX9 – 15 April 2011
Multichannel Buffered Serial Port (McBSP)
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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