Maxim Integrated MAXQ7666 - Manual (Page 188)

MAXQ7665/MAXQ7666 User’s Guide
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Case 2: Software-Initiated Reply
(Using TIH as gating control.) CAN module wants to receive an RFR and wait for software to determine when and what is transmitted
in reference to RFR.
1) Software sets T/ R = 1, MSRDY = 0, DTUP = 0, and TIH = 1.
2) Software 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 pre-
viously 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 automatically transmits data (as per RFR DTBYC) in respective message center.
12) CAN clears EXTRQ = 0 and MTRQ = 0.
Case 3: Software-Initiated Reply
(Reply through same message center, using TIH as gating control.) CAN module wants to receive an RFR in a receive-configured (T/ R
= 0) message center. When the data is received, the message center is reconfigured to 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 previously completed transmission.
2) CAN successfully receives RFR.
3) CAN forces EXTRQ = 1 and DTUP = 1.
4) MTRQ cannot be written to 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.
6) CAN waits for software to read message center and determine the fact that EXTRQ = 1.
7) Software disables message center and converts message center into transmit message center.
a. Software clears MSRDY = 0 to disable message center. Software leaves EXTRQ = 1.
b. Software then forces message center to transmit mode, T/ R = 1.
8) Software writes MSRDY = 0, DTUP = 0, and TIH = 1 in preparation to load data.
9) Software loads data into message center.
10) Software writes MSRDY = 1, MTRQ = 1, DTUP = 1, and TIH = 0 in same instruction. Note: Software leaves EXTRQ = 1.1
11) CAN automatically transmits data (as per RFR DTBYC) in respective message center.
12) CAN clears EXTRQ = 0 and MTRQ = 0.
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