I'm deep in the forest of CAN bus, and I suspect too close (Drilled down) to the problem to see what it really is. I have 51 CAN nodes that should intercommunicate. 48 detectors, 2(4) nodes on the LINUX engine, and 1 pushbutton board. We are using 2 dual PC-104 can boards on the LINUX engine for 4 different CAN buses, but we could use only one PC-104 board I can get this bus fixed. I have an application note from Analog devices that states that you can only have 40 nodes on a bus. With the MINIMUM bus specification, I see 11 bits for bus node ID., so I ASSUMED you could assign several THOUSAND nodes per bus. With our current 4 bus scheme, one end of the bus is a 120 ohm terminated node (PC-104 or CAN diagnostic tool) I have 122 ohm twisted pair going to 2 groups of 6 nodes in daisy chain, and then a 120 ohm termination at the end of the bus . The group of 6 nodes is NOT daisy chained, but are designed as two 3" long star stubs on the chain. Bench testing reveals more tantalizing clues... All nodes work well for the first 900 or so messages. then the lowest and highest ID nodes in each group of 6 stall, while the middle 4 (ID) nodes continue chugging on. The stalled nodes make some attempt to catch up, but eventually the software FIFOs fill up with unsent messages. It make no difference what ID I assign to the failing nodes. I think I might hack the PC boards and even daisy chain the groups as this seems (to me) to be a physical layout problem. (Why it takes 900 messages to fail, is an argument against a physical layout problem.) But the highest and lowest ID nodes are the most physically distant (6") in the star stub. (They are on 2 different PC boards, connected via a common node group PC board.) I could also wire it up as 4 groups of 3 star nodes I know this is complicated, and if I knew then what I know now.... I would have designed it as all daisy chain. (But I read the spec. allowing nodes to be quite long off the bus relative to the 3 inches I am using in my nodes.) YAP wrote: >On 4/25/07, Thomas C. Sefranek wrote: > > >>Hi Group, >>Is there anyone out there with a working knowledge of the CAN bus and the >>18F4585? >> >> I have it working with 25 nodes, but it has some Curious failures about >>.25% of the time. (Extended messages, null messages...) >>It looks like unresolved collisions in messages. >>I've tried lower baud rates and still have the problem. >> >>I'm using 122 ohm twisted pair, terminated at both ends. >>The signals look good on a "scope" at 1 megabaud. >> >>Tom >> >> > > >Have you checked the errdata? > >+Under specific conditions, the first five bits of a >+transmitted identifier may not match the value in >+the Transmit Buffer ID register, TXBnSIDH. The >+following conditions must exist for the corruption to >+occur: >+1. A transmit message must be pending. >+2. The ECAN module must detect a Start-of- >+Frame (SOF) in the third bit of interframe >+space. > >May be the problem. In my setups I have seen this as random id's from >time to time. Never seen it using the non ECAN mode. > >/Ake > > > > > > > >> * >> | __O Thomas C. Sefranek WA1RHP@ARRL.NET >> |_-\<,_ Amateur Radio Operator: WA1RHP >> (*)/ (*) Bicycle mobile on 145.41MHz PL74.4 >> >>ARRL Instructor, Technical Specialist, VE Contact. >>http://hamradio.cmcorp.com/inventory/Inventory.html >>http://www.harvardrepeater.org >> >> >>-- >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> > > > > -- * | __O Thomas C. Sefranek WA1RHP@ARRL.net |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz http://hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist