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Frequently asked questions

Industrial UART Status Register FAQ

Q What is the difference between RxRDY and FFULL in the Status Register?
A
RxRDY is set when at least one byte remains in the Rx FIFO. RxRDY is cleared and when the Rx FIFO is empty.
FFULL is set when the Rx FIFO is full (at maximum bytes) and cleared when the Rx FIFO is not full.
Q What is the difference between RxRDY in SR and RxRDY in ISR?
A
RxRDY in SR indicates that there is at least one byte in the RxFIFO.
RxRDY in ISR indicates the RxFIFO is at or above the programmed RxFIFO interrupt fill level. If the Rx interrupt is set in the IMR, the Rx will be arbitrating for an interrupt.
Q What is the difference between TxRDY and TxEMT in the status register?
A
TxRDY is set when there is at least one byte empty in the TxFIFO and cleared when the TxFIFO is full (at maximum bytes).
TxEMT is set when the TxFIFO is empty and cleared when the TxFIFO is not empty.
Q What is the difference between TxRDY in SR and TxRDY in ISR?
A
TxRDY in SR indicates that the TxFIFO has at least one byte empty in the TxFIFO.
TxRDY in ISR indicates that the TxFIFO is at or below the programmed TxFIFO interrupt fill level. If the Tx interrupt is set in the IMR, the Tx will be arbitrating for an interrupt.
Q What is an Overrun error in SR?
A It indicates at least one byte in the received data stream has been lost. If the bit is set, a new byte is lost when the RxFIFO is full.
Q What is a Parity error in SR?
A It indicates a received byte with incorrect parity in the with parity or force parity mode.
Q What is a Framing error in SR?
A It indicates a stop bit is not detected.
Q What is a Received Break?
A It indicates an all zero character has been received without a stop bit.
Q What is multi-drop mode?
A It is also called 9-bit or wake-up mode and operates as follows:
  • The master sends an address byte followed by data bytes for the addressed slave.
  • The slave's receiver accepts data after a valid address is received.
  • The parity bit is used as an address or data indicator.

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