Texas Instruments TMS320C6201 Reference Manual page 363

11.3.7.3 Transmit With Data Overwrite
Figure 11–28. Transmit With Data Overwrite
CLKX
FSX
DX
A1 A0
XRDY
DXR-to-XSR copy (B)
11.3.7.4 Transmit Empty: XEMPTY
Figure 11–28 shows what happens if the data in DXR is overwritten before it is
transmitted. Suppose you load the DXR with data C. A subsequent write to the
DXR overwrites C with D before C is copied to the XSR. Thus, C is never trans-
mitted on DX. The CPU can avoid overwriting data by polling XRDY before writ-
ing to DXR or by waiting for a programmed XINT to be triggered by XRDY
(XINTM = 00b). The DMA controller can avoid overwriting by synchronizing data
writes with XEVT.
B7 B6 B5
Write of DXR (C)
XEMPTY indicates whether the transmitter has experienced under flow. Either
of the following conditions causes XEMPTY to become active (XEMPTY = 0):
During transmission, DXR has not been loaded since the last DXR-to-XSR
copy, and all bits of the data element in the XSR have been shifted out on
DX.
The transmitter is reset (XRST = 0 or the device is reset) and then re-
started.
During underflow condition, the transmitter continues to transmit the old data
in DXR for every new frame sync signal that arrives on FSX until a new element
is loaded into DXR by the CPU or the DMA controller. XEMPTY is deactivated
(XEMPTY = 1) when this new element in DXR is transferred to XSR. In the
case of internal frame sync generation, the transmitter regenerates a single
FSX initiated by a DXR-to-XSR copy (FSXM = 1 in the PCR and FSGM = 0 in
SRGR). Otherwise, the transmitter waits for the next frame synchronization.
B4 B3 B2 B1 B0
Write of DXR (D) DXR-to-XSR copy (D)
Multichannel Buffered Serial Ports
Data Transmission and Reception
D7 D6
Write of DXR (E)
11-45