Other Parts Discussed in Thread: HALCOGEN, SN65HVD266
I am working on a system that uses two Hercules MCUs connected via a CAN bus using SN65HVD266 transceivers. The CAN modules for both Hercules devices are configured in Halcogen as follows:
Bite rate: 125 Kbit/s
prop delay: 1000ns
sample point of reference: 70%
CAN input freq. (VCLKA1) 100 Mhz
The intent is for the system to support a max cable length of 1500' but for this test the cable is 25' long.
Looking at the CAN bus with a differential probe I occasionally see that frames do not get an ack bit. These are marked by my scope and I see a subsequent retransmission of the frame that does get acked.
In the scope traces that follow Ch1 and Ch2 are the TTL Tx/Rx signals at the transceiver on the receiving end of this transmission and Ch4 is from a differential probe on the CAN bus at the transmitting end.
This plot shows an unacked frame followed by a retransmit that gets acked.
This plot shows details of the missing ACK and the receiver signalling frame error.
This plot show details of the retransmitted frame with an ACK generated by the receiver.
This plot includes the TTL Tx signal at the transmitting side to illustrate the prop delay from transmitter Tx signal to Receiver Rx signal.
What would prevent the receiving CAN module from acking this frame given that the data at it's Rx pin appears to match the transmitted differential data?