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Chapter 32 USART (LIN / FIFO)
7.USART Operation
Figure 7-7 LIN bus timing and USART signals
7.4 Direct Access to Serial Pins
USART allows the user to access directly the transmission pin (SOT04) or the reception pin (SIN04).
■ USART Direct Pin Access
The USART provides the ability for the user to directly access the serial input or output pin. The software can
always monitor the incoming serial data by reading the SIOP bit of the ESCR04. If setting the Serial Output
Pin direct access Enable (SOPE) bit of the ESCR04 the software can force the SOT04 pin to a desired value.
Note, that this access is only possible, if the transmission shift register is empty (i. e. no transmission activity).
In LIN mode this function can be used for reading back the own transmission and is used for error handling if
something is physically wrong with the single-wire LIN-bus.
(Note) Write the desired value to the SIOP pin before enabling the output pin access, to prevent undesired
peaks. The peaks can occur because SIOP holds the last written value.
During a Read-Modify-Write operation the SIOP bit returns the actual value of the SOT04 pin in the read cycle
instead the value of SIN04 during a normal read instruction.
LIN
bus
RXE
LBD
(IRQ0)
LBIE
RDRF
RIE
old serial clock
no clock used
(calibration frame)
new (calibrated) serial clock
LIN break detected and Interrupt
IRQ from ICU
IRQ from ICU
Reception enable
Edge of Start bit of Identifier byte
Byte read in RDR
RDR read by CPU
ICU count
Reception Interrupt enable
LIN break begins
Read
RDR
by CPU
(SIN)
(IRQ0)
LBIE disable
Internal
IRQ from
IRQ cleared by CPU (LBD -> 0)
ICU
IRQ cleared: Begin of Input Capture
IRQ cleared: Calculate & set new baud rate
Signal
to ICU