ENA INT
x
INT1
...
INT0
FLAG
x
INT
x
LVL
...
...
Priority
Encoder 0
...
Priority
Encoder 1
5-bit
INTVECT0
5-bit
INTVECT1
SCI Interrupts
1333
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Serial Communication Interface (SCI) Module
Figure 26-7. Interrupt Generation for Given Flags
26.3.1 Transmit Interrupt
To use transmit interrupt functionality, SET TX INT bit must be enabled and SET TX DMA bit must be
cleared. The transmit ready (TXRDY) flag is set when the SCI transfers the contents of SCITD to the shift
register, SCITXSHF. The TXRDY flag indicates that SCITD is ready to be loaded with more data. In
addition, the SCI sets the TX EMPTY bit if both the SCITD and SCITXSHF registers are empty. If the SET
TX INT bit is set, then a transmit interrupt is generated when the TXRDY flag goes high. Transmit Interrupt
is not generated immediately after setting the SET TX INT bit unlike transmit DMA request. Transmit
Interrupt is generated only after the first transfer from SCITD to SCITXSHF, that is first data has to be
written to SCITD by the User before any interrupt gets generated. To transmit further data the user can
write data to SCITD in the transmit Interrupt service routine.
Writing data to the SCITD register clears the TXRDY bit. When this data has been moved to the
SCITXSHF register, the TXRDY bit is set again. The interrupt request can be suspended by setting the
CLR TX INT bit; however, when the SET TX INT bit is again set to 1, the TXRDY interrupt is asserted
again. The transmit interrupt request can be eliminated until the next series of values is written to SCITD,
by disabling the transmitter via the TXENA bit, by a software reset SWnRST, or by a device hardware
reset.
26.3.2 Receive Interrupt
The receive ready (RXRDY) flag is set when the SCI transfers newly received data from SCIRXSHF to
SCIRD. The RXRDY flag therefore indicates that the SCI has new data to be read. Receive interrupts are
enabled by the SET RX INT bit. If the SET RX INT is set when the SCI sets the RXRDY flag, then a
receive interrupt is generated. The received data can be read in the Interrupt Service routine.
On a device with both SCI and a DMA controller, the bits SET RX DMA ALL and SET RX DMA must be
cleared to select interrupt functionality.
26.3.3 WakeUp Interrupt
SCI sets the WAKEUP flag if bus activity on the RX line either prevents power-down mode from being
entered, or RX line activity causes an exit from power-down mode. If enabled (SET WAKEUP INT),
wakeup interrupt is triggered once WAKEUP flag is set.