Information

4. If a valid edge is not identified before the delay time expires, and data is queued to be

transmitted, the UART considers itself synchronized, and starts the preamble

process.

5. If a valid edge is not identified before the delay time expires, and data is not queued

to be transmitted, the UART continues attempting to locate a valid edge using the

same process, and receives the incoming data packet like in step 3.

RESET

INIT

WAIT1

WAIT2

lonen &!INITF

INIT DETECT

Beta1 Expired

SDT Expired & txen

Preamble Start

LCV end detect

TX done

pct expired

INITF = 1’b1

45.4.1.6 Priority packet preemption

The first data is fetched from the data buffer immediately after the preamble has

completed. Therefore, it is possible to decide which data is sent during transmission until

the completion of the preamble. This can be done in two different ways.

• The expected data to be transmitted can be written to the data buffer before or shortly

after TE is enabled. In this case, the data is ready before the start of the preamble

period. If a high priority packet has been identified for immediate/preemptive

transmission, software may flush the data buffer and put the new data into the data

buffer. This new data must be put into the data buffer prior to the completion of the

preamble. Similarly, the transmit packet length register needs to be updated.

• Software can trigger data to be transmitted by asserting TE before the actual data has

been placed in the data buffer. In the end, the software can write data into the data

buffer and update the transmit packet length register. This occurs before the

preamble completes. To assist in identifying how much time is left before the

Functional description

K20 Sub-Family Reference Manual, Rev. 2, Feb 2012

1106 Freescale Semiconductor, Inc.