AN1278 datasheet(39/44 Pages) STMICROELECTRONICS

39 / 44 page

39/44

LIN (LOCAL INTERCONNECT NETWORK) SOLUTIONS

4.4.2.1 Reception

The SCI is emulated by software using the input capture and output compare of the on-chip

16-bit timer. When the bus is idle, the software waits for a negative edge: The input capture in-

terrupt is activated and calls the LIN interrupt when a negative edge occurs. The input capture

time is used to generate an output compare in the middle of this first bit. The LIN interrupt rou-

tine returns to the calling program. When the output compare event occurs the LIN interrupt is

called again. The bus level is checked and a new output compare is set to occur in the middle

of the next bit. This last process is repeated until the stop bit.

As a result the application software should not:

– delay the occurrence of the IC interrupt too much. Specifically: A problem occurs if the first

output compare is set after the expected occurrence of the output compare event, which is

the middle of the bit. So as long as the IC interrupt ends before the middle of the bit, the delay

is acceptable. See Figure 18.

Figure 18. IC Interrupt Handing in Reception Mode

– Delay the occurrence of each OC interrupt too much. Specifically: A problem occurs if the

sample time defined at the beginning of the interrupt is delayed so that it occurs after the end

of the bit. See Figure 19.

start bit

application task

IC request IC interrupt served

deadline for

end of IC interrupt

1/2

AN1278 数据表(PDF) 39 Page - STMicroelectronics