SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
To use transmit interrupt functionality, SETTXINT bit must be enabled and SET_TX_DMA bit must be cleared in the SCISETINT register. The transmit ready (TXRDY) flag is set when the SCI transfers the contents of SCITD/TDy to the shift register, SCITXSHF. The TXRDY flag indicates that SCITD/TDy is ready to be loaded with more data. In addition, the SCI sets the TX EMPTY bit if both the SCITD/TDy and SCITXSHF registers are empty. If the SETTXINT bit is set, then a transmit interrupt is generated when the TXRDY flag goes high. The transmit interrupt is not generated immediately after setting the SETTXINT bit unlike the transmit DMA request. The transmit interrupt is generated only after the first transfer from SCITD/TDy to SCITXSHF, that is first data has to be written to SCITD/TDy before any interrupt gets generated. To transmit further data, data can be written to SCITD/TDy in the transmit interrupt service routine.
Writing data to the SCITD/TDy 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 CLRTXINT bit in the SCICLEARINT register; however, when the SETTXINT 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/TDy, by disabling the transmitter using the TXENA bit, by a software reset SWnRST, or by a device hardware reset.