When FSR and FSX are outputs, implying that they are driven by the sample rate generator, they are generated
(transition to their active state) on the rising edge of internal clock, CLK(R/X). Similarly, data on the DX pin is
output on the rising edge of internal CLKX.
FSRP, FSXP, CLKRP, and CLKXP in the pin control register (PCR) configure the polarities of the FSR, FSX,
MCLKR, and CLKX signals, respectively. All frame-synchronization signals (internal FSR, internal FSX) that are
internal to the serial port are active high. If the serial port is configured for external frame synchronization
(FSR/FSX are inputs to McBSP), and FSRP = FSXP = 1, the external active-low frame-synchronization
signals are inverted before being sent to the receiver (internal FSR) and transmitter (internal FSX). Similarly,
if internal synchronization (FSR/FSX are output pins and GSYNC = 0) is selected, the internal active-high
frame-synchronization signals are inverted, if the polarity bit FS(R/X)P = 1, before being sent to the FS(R/X) pin.
On the transmit side, the transmit clock polarity bit, CLKXP, sets the edge used to shift and clock out transmit
data. Data is always transmitted on the rising edge of internal CLKX. If CLKXP = 1 and external clocking is
selected (CLKXM = 0 and CLKX is an input), the external falling-edge triggered input clock on CLKX is inverted
to a rising-edge triggered clock before being sent to the transmitter. If CLKXP = 1 and internal clocking is
selected (CLKXM = 1 and CLKX is an output pin), the internal (rising-edge triggered) clock, internal CLKX, is
inverted before being sent out on the MCLKX pin.
Similarly, the receiver can reliably sample data that is clocked with a rising edge clock (by the transmitter).
The receive clock polarity bit, CLKRP, sets the edge used to sample received data. The receive data is always
sampled on the falling edge of internal MCLKR. Therefore, if CLKRP = 1 and external clocking is selected
(CLKRM = 0 and CLKR is an input pin), the external rising-edge triggered input clock on CLKR is inverted to
a falling-edge triggered clock before being sent to the receiver. If CLKRP = 1 and internal clocking is selected
(CLKRM = 1), the internal falling-edge triggered clock is inverted to a rising-edge triggered clock before being
sent out on the MCLKR pin.
CLKRP = CLKXP in a system where the same clock (internal or external) is used to clock the receiver and
transmitter. The receiver uses the opposite edge as the transmitter to ensure valid setup and hold of data around
this edge (see
).
shows how data clocked by an external serial device using a rising edge can be sampled by the
McBSP receiver on the falling edge of the same clock.
B6
B7
DR
CLKR
Data hold
ÁÁ
ÁÁ
ÁÁ
ÁÁ
Data setup
Internal
Figure 15-60. Data Clocked Externally Using a Rising Edge and Sampled by the McBSP Receiver on a
Falling Edge
Multichannel Buffered Serial Port (McBSP)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
953
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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