Frames And Frame Synchronization - Texas Instruments TMS320VC5501 Reference Manual

Clocking and Framing Data
Internal
CLK(R/X)
Internal
FS(R/X)
Á
A1 A0
D(R/X)
Á
2.3.3

Frames and Frame Synchronization

Internal
CLK(R/X)
Internal
FS(R/X)
Á
A1 A0
D(R/X)
Á
2-8 McBSP Operation
During transmission, XSR does not accept new data from DXR until a full serial
word has been passed from XSR to the DX pin.
In the following example, an 8-bit word size was defined (see bits 7 through
0 of word B being transferred).
Á
B7 B6
Á
One or more words are transferred in a group called a frame. You 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
(frame-sync) signals to determine when each frame is received/transmitted.
When a pulse occurs on a frame-sync 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-sync signal (FSR) initiate frame transfers on DR.
Pulses on the transmit frame-sync signal (FSX) 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.
In the following example, a 1-word frame is transferred when a frame-sync
pulse occurs.
Á
B7 B6
Á
In McBSP operation,
frame-synchronization signal indicates the start of the next frame. For this
reason, the frame-sync 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.
B5 B4 B3 B2 B1
B5 B4 B3 B2 B1
the inactive-to-active
Á
B0
Á
Á
B0
Á
transition of the
SPRU592E