Maxim Integrated MAXQ7666 - Manual (Page 192)

MAXQ7665/MAXQ7666 User’s Guide
4-62
The autobaud feature for the CAN module is enabled by setting the autobaud bit (C0C.2). Setting this bit activates a special loopback
circuit within the CAN module that logically ANDs incoming network data received on the Rx pin with the Tx pin of the CAN module.
While the autobaud bit is set, the CAN module disables its transmit output and places it in the recessive (high) state, so that error
frames generated by the autobauding CAN module do not disturb other devices on the network during the procedure. Figure 4-13 out-
lines the CAN autobaud feature.
The following user-defined software procedure can be used with the autobaud feature to determine the baud rate of the network.
1) Set CRST = 1 to disable bus activity. Setting this bit also sets the SWINT bit, enabling access to control/status registers, and
also clears the C0RE and C0TE registers.
2) Configure bus timing registers to set desired baud rate.
3) Set autobaud bit = 1.
4) Set SWINT = 0 to enable CAN module and begin listening for errors.
5) Delay approximately 500ms (allow enough time for > 128 errors to occur).
6) If CAN error-count-exceeded (EC96/128) bit is set, baud rate is incorrect. Select a new baud rate and repeat procedure. If
EC96/128 bit is not set, the MAXQ7665/MAXQ7666 CAN module is set to the correct baud rate.
Figure 4-13. CAN Autobaud Feature
RECEIVE
Rx
CAN
PROCESSOR
CAN 0 CONTROL REGISTER
ERIE STIE PDE CRST SIESTA AUTOB ERC3 SWINT Tx
TRANSMIT
Maxim Integrated