Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 145)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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Case 1: Automatic Reply
CAN Controller receives a remote frame Request (RFR) and automatically transmits data without
additional software intervention.
1. Software sets T/ R = 1, MSRDY = 0, DTUP = 0, and TIH = 1.
2. Software loads data into respective message center.
3. Set WTOE.
4. Software sets MSRDY = 1, DTUP = 1 and TIH = 0 in same instruction.
Note: Software does not change MTRQ = 0 from previous completed transmission
5. CAN does not transmit data (MTRQ = 0), but waits for RFR.
6. CAN successfully receives RFR.
7. CAN forces MTRQ = 1 and EXTRQ = 1
8. CAN loads DTBYC from RFR and ID into arbitration registers.
9. CAN automatically transmits data in respective message center.
10. CAN clears EXTRQ = 0 and MTRQ = 0.
Case 2: Software-Initiated Reply (Using TIH as Gating Control)
CAN module wishes to receive an RFR and wait for software to determine when and what will be
transmitted in reference to RFR.
1. Software sets T/ R = 1, MSRDY = 0, DTUP = 0, and TIH = 1.
2. Software then loads data into respective message center.
3. Software sets MSRDY = 1, DTUP = 1 and TIH = 1 in same instruction.
Note: Software does not change MTRQ = 0 from previous completed transmission
4. CAN does not transmit data (MTRQ = 0), but waits for RFR.
5. CAN successfully receives RFR.
6. CAN forces MTRQ = 1 and EXTRQ = 1.
7. CAN loads DTBYC from RFR and ID into arbitration registers.
8. CAN waits for software to read message center and determine the fact that EXTRQ = 1.
9. Software may load data into message center (or it may already have the data established).
10. Software writes MSRDY = 1, DTUP = 1 and TIH = 0 in same instruction.
11. CAN will automatically transmit data (as per RFR DTBYC) in respective message center.
12. CAN clears EXTRQ = 0 and MTRQ = 0.
Case 3: Software-Initiated Reply (Reply by same message center, using TIH as Gating Control)
CAN module wishes to receive an RFR in a receive-configured (T/ R = 0) message center. When the data
is received, the message center will be reconfigured send data back to the remote request node. This
relationship is not possible for message center 15.
1. Software sets T/ R = 0, MSRDY = 1, and DTUP = 0 and awaits either data frame or RFR.
Note: Software does not change MTRQ = 0 from previous completed transmission
2. CAN successfully receives RFR.
3. CAN forces EXTRQ = 1 and DTUP = 1.
4. MTRQ can not be written to a 1 by the CAN when T/ R = 0 and is left as MTRQ = 0
5. CAN loads DTBYC from RFR and ID into arbitration registers.