• Case 2: Normal serial port transmission. Transmission continues normally because the frame-synchronization
pulse is not unexpected. There are two possible reasons why a transmit operations might
not
be in progress
when the pulse occurs:
This FSX pulse is the first after the transmitter is enabled (XRST = 1).
The serial port is in the interpacket intervals. The programmed data delay for transmission (programmed with
the XDATDLY bits of XCR2) may start during these interpacket intervals before the first bit of the previous
word is transmitted. Thus, at maximum packet frequency, frame synchronization can still be received 0 to 2
clock cycles before the first bit of the synchronized frame.
• Case 3: Unexpected transmit frame synchronization with XFIG = 0 (frame-synchronization pulses not
ignored). Unexpected frame-synchronization pulses can originate from an external source or from the internal
sample rate generator.
If a frame-synchronization pulse starts the transfer of a new frame before the current frame is fully
transmitted, this pulse is treated as an unexpected frame-synchronization pulse, and the transmitter sets
the transmit frame-synchronization error bit (XSYNCERR) in SPCR2. XSYNCERR can be cleared only by a
transmitter reset or by a write of 0 to this bit.
If you want the McBSP to notify the CPU of frame-synchronization errors, you can set a special transmit
interrupt mode with the XINTM bits of SPCR2. When XINTM = 11b, the McBSP sends a transmit interrupt
(XINT) request to the CPU each time that XSYNCERR is set.
15.4.5.2 Example of Unexpected Transmit Frame-Synchronization Pulse
shows an unexpected transmit frame-synchronization pulse during normal operation of the serial
port with intervals between the data packets. When the unexpected frame-synchronization pulse occurs, the
XSYNCERR bit is set and the transmission of data B is restarted because no new data has been passed to
XSR1 yet. In addition, if XINTM = 11b, the McBSP sends a transmit interrupt (XINT) request to the CPU.
Á
Á
Á
B0
B1
B2
B3
B4
B5
B6
B7
B4
B5
B6
B7
A0
A1
XSYNCERR
XRDY
DX
FSX
CLKX
Á
Á
Á
Á
Á
Á
Write to DXR1(D)
DXR1 to XSR1 (C)
Write to DXR1(C)
DXR1 to XSR1 copy(B)
Unexpected frame synchronization
Figure 15-30. An Unexpected Frame-Synchronization Pulse During a McBSP Transmission
15.4.5.3 Preventing Unexpected Transmit Frame-Synchronization Pulses
Each frame transfer can be delayed by 0, 1, or 2 CLKX cycles, depending on the value in the XDATDLY bits of
XCR2. For each possible data delay,
shows when a new frame-synchronization pulse on FSX can
safely occur relative to the last bit of the current frame.
Multichannel Buffered Serial Port (McBSP)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
903
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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