Texas Instruments TMS320C3x - Manual (Page 419)

Serial Ports
12-40
- Variable Standard Mode
When you transmit continuously in variable data-rate mode with frame sync,
timing is the same as for fixed data-rate mode, except for the differences
between these two modes as described in Section 12.2.12
Serial-Port
Functional Operation, on page 12-35. The only other exception is that you
must reload DXR no later than the
N–4 bit to maintain continuous opera-
tion of the variable data-rate mode (see Figure 12–31); you must reload
DXR no later than the
N–3 bit to maintain continuous operation of the fixed
data-rate mode.
Figure 12–31. Variable Standard Mode With Back-to-Back Frame Syncs
DXR
Loaded
with A
XINT
Load DSR
with B
XINT
RINT
Load DXR with C
Read DRR
XINT
RINT
Load DXR with D
Read DRR
CLKX/R
FSR/FSX (External)
FSX (Internal)
DX/DR A1 AN B1 BN C1 C2
R/XVAREN = 1
R/XFSM = 0
Continuous operation in variable data-rate mode without frame sync (see
Figure 12–32) is similar to continuous operation without frame sync in
fixed data-rate mode (see Figure 12–28). As with variable data-rate stan-
dard mode with back-to-back frame syncs, you must reload DXR no later
than the
N–4 bit to maintain continuous operation. Additionally, when
R/XFSM is set or cleared in the variable data-rate mode, you must make
the modification no later than the
N–1 bit for the result to be affected in the
current transfer.