LIN
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SPNU563A–March 2018
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Serial Communication Interface (SCI)/ Local Interconnect Network (LIN)
Module
29.3.1.9 Message Filtering and Validation
Message filtering uses the entire identifier to determine which nodes will participate in a response, either
receiving or transmitting a response. Therefore, two acceptance masks are used as shown in Figure 29-
24. During header reception, all nodes filter the ID-Field (ID-Field is the part of the header explained in
Figure 29-16) to determine whether they transmit a response or receive a response for the current
message. There are two masks for message ID filtering: one to accept a response reception, the other to
initiate a response transmission. See Figure 29-24. All nodes compare the received ID to the identifier
stored in the ID-SlaveTask BYTE of the LINID register and use the RX ID MASK and the TX ID MASK
fields in the LINMASK register to filter the bits of the identifier that should not be compared.
If there is an RX match with no parity error and the RXENA bit is set, there will be an ID RX flag and an
interrupt will be triggered if enabled. If there is a TX match with no parity error and the TXENA bit is set,
there will be an ID TX flag and an interrupt will be triggered if enabled in the SCISETINT register.
The masked bits become don’t cares for the comparison. To build a mask for a set of identifiers, an XOR
function could be used.
For example, to build a mask to accept IDs 0x26 and 0x25 using LINID[7:0] = 0x20; that is, compare 5
most significant bits (MSBs) and filter 3 least significant bits (LSBs), the acceptance mask could be:
(50)
A mask of all zeros will compare all bits of the received identifier in the shift register with the ID-BYTE in
LINID[7:0]. If HGEN CTRL is set to 1, a mask of 0xFF will always cause a match. A mask of all 1s will
filter all bits of the received identifier, and thus there will be an ID match regardless of the content of the
ID-SlaveTask BYTE field in the LINID register.
NOTE: When the HGEN CTRL bit = 0, the LIN nodes compare the received ID to the ID-BYTE field
in the LINID register, and use the RX ID MASK and the TX ID MASK in the LINMASK
register to filter the bits of the identifier that should not be compared.
If there is an RX match with no parity error and the RXENA bit is set, there will be an ID RX
flag and an interrupt will be triggered if enabled. A mask of all 0s will compare all bits of the
received identifier in the shift register with the ID-BYTE field in LINID[7:0]. A mask of all 1s
will filter all bits of the received identifier and there will be no match.
During header reception, the received identifier is copied to the Received ID field LINID[23:16]. If there is
no parity error and there is either a TX match or an RX match, then the corresponding TX or RX ID flag is
set. If the ID interrupt is enabled, then an ID interrupt is generated.
After the ID interrupt is generated, the CPU may read the Received ID field LINID[23:16] and determine
what response to load into the transmit buffers.
NOTE: When byte 0 is written to TD0 (LINTD0[31:24]), the response transmission is automatically
generated.
In multi-buffer mode, the TXRDY flag will be set when all the response data bytes and checksum byte are
copied to the shift register SCITXSHF. In non-multi-buffer mode, the TXRDY flag is set each time a byte is
copied to the SCITXSHF register, and also for the last byte of the frame after the checksum byte is copied
to the SCITXSHF register.
In multi-buffer mode, the TXEMPTY flag is set when both the transmit buffer(s) TDy and the SCITXSHF
shift register are emptied and the checksum has been sent. In nonmulti-buffer mode, TXEMPTY is set
each time TD0 and SCITXSHF are emptied, except for the last byte of the frame where the checksum
byte must also be transmitted.
If parity is enabled, all slave receiving nodes will validate the identifier using all eight bits of the received
ID byte. The SCI/LIN will flag a corrupted identifier if an ID-parity error is detected.
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