SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
Message filtering uses the entire identifier to determine which nodes 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 3-305) to determine whether the nodes 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-Responder Task 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 can not be compared.
If there is an RX match with no parity error and the RXENA bit is set, there is an ID RX flag and an interrupt is triggered if enabled. If there is a TX match with no parity error and the TXENA bit is set, there is an ID TX flag and an interrupt is 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 can 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 can be:
A mask of all zeros compares 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 always causes a match. A mask of all 1s filters all bits of the received identifier, and thus there is an ID match regardless of the content of the ID-Responder Task BYTE field in the LINID register.
If there is an RX match with no parity error and the RXENA bit is set, there is an ID RX flag and an interrupt is triggered if enabled. A mask of all 0s compares all bits of the received identifier in the shift register with the ID-BYTE field in LINID[7:0]. A mask of all 1s filters all bits of the received identifier and there is no match.
If HGEN CTLR = 1:
If HGEN CTRL = 0:
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 can read the Received ID field LINID[23:16] and determine what response to load into the transmit buffers.
In multibuffer mode, the TXRDY flag is set when all the response data bytes and checksum byte are copied to the shift register SCITXSHF. In non-multibuffer 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 multibuffer mode, the TXEMPTY flag is set when both the transmit buffers TDy and the SCITXSHF shift register are emptied and the checksum has been sent. In non-multibuffer 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 responder receiving nodes validate the identifier using all eight bits of the received ID byte. The SCI/LIN flags a corrupted identifier if an ID-parity error is detected.