While a data transfer is in progress, the SPI hardware sets the BUSY bit. This bit can be polled by the user to determine the current status of the SPI module, and to know when a communication is complete. The following registers and bits will not be changed by software while the BUSY bit is set:
  1. 1.The BUSY bit is subject to synchronization delay of up to two instruction cycles. The user must wait for it to set after loading the transmit buffer (SPIxTXB register) before using it to determine the status of the SPI module.
  2. 2.It is also not recommended to read SPIxTCNT while the BUSY bit is set, as the value in the registers may not be a reliable indicator of the transfer counter. Use the TCZIF bit to accurately determine that the transfer counter has reached zero.