, an 8-bit word size was defined (see bits 7 through 0 of word B being transferred).
15.2.3.3 Frames and Frame Synchronization
One or more words are transferred in a group called a frame. You can define how many words are in a frame.
All of the words in a frame are sent in a continuous stream. However, there can be pauses between
frame transfers. The McBSP uses frame-synchronization signals to determine when each frame is received/
transmitted. When a pulse occurs on a frame-synchronization signal, the McBSP begins receiving/transmitting a
frame of data. When the next pulse occurs, the McBSP receives/transmits the next frame, and so on.
Pulses on the receive frame-synchronization (FSR) signal initiate frame transfers on DR. Pulses on the transmit
frame-sync (FSX) signal initiate frame transfers on DX. FSR or FSX can be derived from a pin at the boundary of
the McBSP or derived from inside the McBSP.
, a one-word frame is transferred when a frame-synchronization pulse occurs.
In McBSP operation, the inactive-to-active transition of the frame-synchronization signal indicates the start of
the next frame. For this reason, the frame-synchronization signal may be high for an arbitrary number of clock
cycles. Only after the signal is recognized to have gone inactive, and then active again, does the next frame
synchronization occur.
15.2.3.4 Generating Transmit and Receive Interrupts
The McBSP can send receive and transmit interrupts to the CPU to indicate specific events in the McBSP. To
facilitate detection of frame synchronization, these interrupts can be sent in response to frame-synchronization
pulses. Set the appropriate interrupt mode bits to 10b (for reception, RINTM = 10b; for transmission, XINTM =
10b).
15.2.3.4.1 Detecting Frame-Synchronization Pulses, Even in Reset State
Unlike other serial port interrupt modes, this mode can operate while the associated portion of the serial port
is in reset (such as activating RINT when the receiver is in reset). In this case, FSRM/FSXM and FSRP/FSXP
still select the appropriate source and polarity of frame synchronization. Thus, even when the serial port is in
the reset state, these signals are synchronized to the CPU clock and then sent to the CPU in the form of RINT
and XINT at the point at which they feed the receiver and transmitter of the serial port. Consequently, a new
frame-synchronization pulse can be detected, and after this occurs the CPU can take the serial port out of reset
safely.
15.2.3.5 Ignoring Frame-Synchronization Pulses
The McBSP can be configured to ignore transmit and/or receive frame-synchronization pulses. To have the
receiver or transmitter recognize frame-synchronization pulses, clear the appropriate frame-synchronization
ignore bit (RFIG = 0 for the receiver, XFIG = 0 for the transmitter). To have the receiver or transmitter ignore
frame-synchronization pulses until the desired frame length or number of words is reached, set the appropriate
frame-synchronization ignore bit (RFIG = 1 for the receiver, XFIG = 1 for the transmitter). For more details on
unexpected frame-synchronization pulses, see one of the following topics:
•
Unexpected Receive Frame-Synchronization Pulse
)
•
Unexpected Transmit Frame-Synchronization Pulse
)
You can also use the frame-synchronization ignore function for data packing (for more details, see
).
Multichannel Buffered Serial Port (McBSP)
884
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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