Datasheet

46.6.10.8.5 Priority Slots
On a channel by channel basis, the protocol supports optional priority. Priority slots, if any, follow immediately after
the Beta1 period that follows the transmission of a packet (see Figure 46-59). The number of priority slots per
channel ranges from 0 to 127.
The number of priority slots in the LON network configuration is defined through the PSNB field of the USAR
T LON
Priority register (US_LONPRIO). And the priority slot affected to the LON node, if any, is defined through
US_LONPRIO.NPS.
46.6.10.8.6 Indeterminate Time
See “comm_type”.
Like Beta1, the IDT value is different depending on what was the previous frame (transmitted or received frame).
IDTRx and IDTTx can be configured respectively through the USART LON IDT Rx register (US_LONIDTRX) and the
USART LON IDT Tx register (US_LONIDTTX).
46.6.10.8.7 End of Frame Condition
The USART configured in LON mode terminates the frame with a 3 t
bit
long Manchester code violation. After sending
the last CRC bit, it maintains the data transitionless during three bit periods.
While receiving data the USART configured in LON mode will detect an end of frame condition after a t
eof
transitionless Manchester code violation. US_LONMR.EOFS can configure t
eof
.
46.6.10.9 LON Errors
All these flags can be read in the Channel Status register (LON_MODE) (US_CSR) and will generate interrupts if
configured in the Interrupt Enable register (LON_MODE) (US_IER ).
These flags can be reset through US_CR.RSTSTA.
46.6.10.9.1 Underrun Error
If the USART is in LON mode and if a character is sent while the Transmit Holding register (US_THR) is empty, the
UNRE bit flag is set.
46.6.10.9.2 Collision Detection
The LCOL flag is set whenever a valid collision has been detected and the LON node is configured to report it (see
“Collision Detection”).
46.6.10.9.3 LON Frame Early Termination
The LFET flag is set whenever a LON frame has been terminated early due to collision detection.
46.6.10.9.4 Reception Error
The LCRCE flag is set if the received frame has an erroneous CRC and the flag LSFE is set if the received frame is
too short (LON frames must be at least 8 bytes long).
These flags can be read in US_CSR.
46.6.10.9.5 Backlog Overflow
The LBLOVFE flag is set if the LON node backlog estimation goes over 63 which is the maximum backlog value.
46.6.10.10 Drift Compensation
While receiving a frame, the baud rate used by the sender may not be exactly the one expected. In this case, the
hardware drift compensation algorithm recovers up to 16% clock drift (expected baud rate ±16% will be supported).
Drift compensation is available only in 16X Oversampling mode. To enable the hardware system, US_MAN.DRIFT
must be set. If the RXD edge is between one and three 16X clock cycles far from the expected edge, then the period
is shortened or lengthened accordingly, to center the RXD edge.
The drift compensation hardware feature allows up to 16% clock drift to be handled, provided the system clock is fast
enough compared to the selected baud rate.
SAM E70/S70/V70/V71 Family
Universal Synchronous Asynchronous Receiver T
ransc...
© 2019 Microchip T
echnology Inc.
Datasheet
DS60001527D-page 1224