Architecture
1205
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.5.4.3 Transmit Frame Synchronization Selection: FSXM and FSGM
shows how you can select the source of the transmit frame synchronization signal. The three
choices are:
•
External frame sync input
•
The sample rate generator frame sync signal, FSG
•
A signal that indicates a DXR-to-XSR copy has been made
NOTE:
FSR_int and FSX_int are shown in
Table 25-6. Transmit Frame Synchronization Selection
FSXM Bit
in PCR
FSGM Bit
in SRGR
Source of Transmit Frame Synchronization
FSX Pin Function
0
X
External frame sync input on the FSX pin. This is
inverted by FSXP before being used as FSX_int.
Input.
1
1
Sample rate generator frame sync signal (FSG)
drives FSX_int. FRST = 1.
Output. FSG is inverted by FSXP before being
driven out on FSX.
1
0
A DXR-to-XSR copy activates transmit frame sync
signal.
Output. 1-bit-clock-wide signal inverted as
determined by FSXP before being driven out on
FSX.
25.2.5.4.4 Frame Detection
To facilitate detection of frame synchronization, the receive and transmit CPU interrupts (RINT and XINT)
can be programmed to detect frame synchronization by setting the RINTM and XINTM bits in the serial
port control register (SPCR) to 10b. The associated portion (receiver/transmitter) of the McBSP must be
out of reset.
25.2.5.5 Data and Frames
25.2.5.5.1 Frame Synchronization Phases
Frame synchronization indicates the beginning of a transfer on the McBSP. The data stream following
frame synchronization can have up to two phases, phase 1 and phase 2. The number of phases can be
selected by the phase bit, (R/X)PHASE, in RCR and XCR. The number of elements per frame and bits per
element can be independently selected for each phase via (R/X)FRLEN1/2 and (R/X)WDLEN1/2,
respectively.
shows a frame in which the first phase consists of two elements of 12 bits, each
followed by a second phase of three elements of 8 bits each. The entire bit stream in the frame is
contiguous; no gaps exist either between elements or phases.
shows the fields in the
receive/transmit control registers (RCR/XCR) that control the frame length and element length for each
phase for both the receiver and the transmitter. The maximum number of elements per frame is 128 for a
single-phase frame and 256 elements in a dual-phase frame. The number of bits per element can be 8,
12, 16, 20, 24, or 32.
NOTE:
For a dual-phase frame with internally generated frame synchronization, the maximum
number of elements per phase depends on the word length. This is because the frame
period, FPER, is only 12-bits wide and, therefore, provides 4096 bits per frame. Hence, the
maximum number of 256 elements per dual- phase frame applies only when the WDLEN is
16 bits. However, any combination of element numbers and element size (defined by the
FRLEN and WDLEN bits, respectively) is valid as long as their product is less than or equal
to 4096 bits. This limitation does not apply for dual-phase with external frame sync.