The acceptance filter ID registers (AFIR) contain identifier bits, which are used for acceptance filtering. There are four read/write acceptance filter ID registers. These registers should only be written when the corresponding UAF bits in the SR register are 0 and the [ACFBSY] bit in the SR register is 0.
TIP: Proper programming of the TXFIFO_ID and RXFIF_ID [IDE] bits for standard and extended frames must be followed. Setting the [AIIDE] bit in AMIR register to 0 implies that there is only a standard frame ID check.