14.11.5 Transmit Event FIFO Behavior

CxTEFCON is used to control the TEF. CxTEFSTA contains the status flags. CxTEFUA contains the user address of the next message object to read.

The actual RAM address is calculated using Equation 14-25.

Figure 14-40 through Figure 14-47 illustrate how the status flags and user address are updated. The TEF stores transmitted messages; therefore, the flags behave similarly to an RX FIFO.

Figure 14-40 shows the status of the TEF after the Reset. Message objects, MO0 to MO11, are empty. All status flags are cleared. The user address points to MO0.

Figure 14-40. TEF – Initial State

Figure 14-41 shows the status of the TEF after the first transmit message is stored. MO0 contains ID0, the ID of MSG0. TEFNEIF is set since the TEF is not empty. The user address points to MO0.

Figure 14-41. TEF – First Transmit Message is Stored

Figure 14-42 illustrates the status of the TEF after ID0 is read. The user application reads the ID from RAM and sets the UINC bit (CxTEFCON[8]). The user address increments and points to MO1. The TEF is empty again. All flags are cleared.

Figure 14-42. TEF – First ID Read

Figure 14-43 illustrates the status of the TEF after six more messages are transmitted: MSG1-MSG6. The user address points to MO1. TEFNEIF and TEFHIF are set because the TEF is now half-full.

Figure 14-43. TEF – Half-Full

Figure 14-44 illustrates the status of the TEF after five more messages are transmitted: MSG7-MSG11. The user address still points to MO1. TEFNEIF and TEFHIF are set.

Figure 14-44. TEF – Almost Full

Figure 14-45 illustrates the status of the TEF after one more message is transmitted: MSG12. All status flags are set because the TEF is full. The user address points to MO1.

Figure 14-45. TEF – Full

Figure 14-46 illustrates the status of the TEF after one more message is transmitted. Since the TEF is already full, an overflow occurs. The ID is discarded, and TEFOVIF is set. The user address remains unchanged.

Figure 14-46. TEF – Overflow

Figure 14-47 illustrates the status of the TEF after the application cleared TEFOVIF and read one more message. TEFFIF is clear because the TEF is not full anymore. The user address points to MO2.

Figure 14-47. TEF – One More ID Read