Table 15-41. Receive Clock Signal Source Selection
DLB in
SPCR1
CLKRM in PCR Source of Receive Clock
MCLKR Pin Status
0
0
The MCLKR pin is an input driven by an external
clock. The external clock signal is inverted as
determined by CLKRP before being used.
Input
0
1
The sample rate generator clock (CLKG) drives
internal MCLKR.
Output. CLKG, inverted as determined by CLKRP, is
driven out on the MCLKR pin.
1
0
Internal CLKX drives internal MCLKR. To
configure CLKX, see
.
High impedance
1
1
Internal CLKX drives internal MCLKR. To
configure CLKX, see
.
Output. Internal MCLKR (same as internal CLKX) is
inverted as determined by CLKRP before being driven
out on the MCLKR pin.
15.7.18 Set the Receive Clock Polarity
Table 15-42. Register Bit Used to Set Receive Clock Polarity
Register
Bit
Name
Function
Type
Reset
Value
PCR
0
CLKRP
Receive clock polarity
R/W
0
CLKRP = 0
Receive data sampled on falling edge of MCLKR
CLKRP = 1
Receive data sampled on rising edge of MCLKR
15.7.18.1 Frame Synchronization Pulses, Clock Signals, and Their Polarities
Receive frame-synchronization pulses can be generated internally by the sample rate generator (see
mode bit, FSRM, in PCR. FSR is also affected by the GSYNC bit in SRGR2. For information about the effects
of FSRM and GSYNC, see
. Similarly, receive clocks can be selected to be inputs or outputs by
programming the mode bit, CLKRM, in the PCR (see
When FSR and FSX are inputs (FSXM = FSRM= 0, external frame-synchronization pulses), the McBSP detects
them on the internal falling edge of clock, internal MCLKR, and internal CLKX, respectively. The receive data
arriving at the DR pin is also sampled on the falling edge of internal MCLKR. These internal clock signals are
either derived from external source via CLK(R/X) pins or driven by the sample rate generator clock (CLKG)
internal to the McBSP.
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
Multichannel Buffered Serial Port (McBSP)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
935
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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