Your setup sound OK to me. +40 nodes should not be a problem if you use standard transceivers. Post your question on the canlist and I am certain that the guys there will help you trace down your problems. You find the list at http://www.canlist.org/ Cheers /Ake On 5/1/07, Tom Sefranek wrote: > 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 > -- --- Ake Hedman (YAP - Yet Another Programmer) eurosource, Brattbergavagen 17, 820 50 LOS, Sweden Phone: (46) 657 413430 Cellular: (46) 73 0533 146 Company home: http://www.dofscandinavia.com Kryddor/Te/Kaffe: http://www.brattberg.com Personal homepage: http://www.dofscandinavia.com/akhe Automated home: http://www.vscp.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist