Issue
- How do the 7793 and 7798 handle retries?
- Improving I/NET sublan communications
- Excessive MCU Lost messages in AMT
- Command Error messages in AMT
Product Line
TAC INET
Environment
- I/NET sublan
- 7793, 7798
Cause
If there are issues on the physical layer of the network, this will effect the reliability of I/NET communications. However, these risks can be lessened with some best practices.
Resolution
Best Practices and Troubleshooting measures to improve sublan communications:
- Ground the 24V line coming into MRs and ASCs
- Connect ground to the earth ground terminal of DPUs and SCUs.
- Bond the shield of the LAN cable all the way through the network, not landing it on any controller anywhere and then tie it to earth ground in one location. (see diagram)
SubLAN Communication Explained:
- The first packet to any sublan device goes out on the primary channel, terminals 1 and 2 of the sublan connector on the 93/98.
- If the device doesn't respond in time, a second packet is sent out on the alternate channel, terminals 4 and 5.
- If there is still no reply, a third packet goes out on the primary
- Finally, if there is still no reply, that device is marked as lost which generates an "MCU Lost" message.
Optional Configuration for only using Terminals 1 and 2:
- If you are using only Terminals 1 and 2 you could be missing 33% of it's retry capacity. If you follow wiring guides and best practices the device will answer on the first packet every time, however if you have not followed the guide all it takes is a little noise to make the retries necessary.
- If you are unable to use a loop configuration, or want to avoid the extra potential for noise and EMI, in stall a jumper on the sublan connector from terminal 1 to 4 and from terminal 2 to 5
- The allows you to get the extra retry, without the extra cable
- This will also function if you have some controllers on channel A and some on Channel B
- The SLI doesn’t have to be at the end of line on sublan communication
