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Hi Folks I am trying to use CAN bus as a communication link in a project. I have a CAN 'Master' connected to the PC and several CAN 'Nodes'. These nodes are based on Motorola HCS12C32 MCU with CAN. I have got the communication working however I find the default maximum transfer of 8 bytes per transaction somewhat limiting. When searching for higher level protocol layers, most of them seem to be quite expensive or complex. I would like to find out if there is any simple low cost higher level layer that could handle messages and so forth greater than 8 bytes? Another question is, the MCU i use has a Identifier Acceptance Register and a Identifier Mask Register, I am a bit confused as to which should I set if I need to filter only one ID, say for example: accept only messages with ID of 0x105. Regds Jay |
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HCS12 and CAN Bus
Started by ●February 12, 2004
Reply by ●February 13, 20042004-02-13
Reply by ●February 13, 20042004-02-13
Reply by ●February 13, 20042004-02-13
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Hi Jay -- Here are a couple more sources. www.microcanopen.com www.micromessaging.com The micro messaging effort seems to still be in birth, but looks quite interesting. 607-656-2597 -----Original Message----- From: hc08jb8 [mailto:] Sent: Thursday, February 12, 2004 10:52 PM To: Subject: [68HC12] HCS12 and CAN Bus Hi Folks I am trying to use CAN bus as a communication link in a project. I have a CAN 'Master' connected to the PC and several CAN 'Nodes'. These nodes are based on Motorola HCS12C32 MCU with CAN. I have got the communication working however I find the default maximum transfer of 8 bytes per transaction somewhat limiting. When searching for higher level protocol layers, most of them seem to be quite expensive or complex. I would like to find out if there is any simple low cost higher level layer that could handle messages and so forth greater than 8 bytes? Another question is, the MCU i use has a Identifier Acceptance Register and a Identifier Mask Register, I am a bit confused as to which should I set if I need to filter only one ID, say for example: accept only messages with ID of 0x105. Regds Jay --------------------To learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu o learn more about Motorola Microcontrollers, please visit http://www.motorola.com/mcu Yahoo! Groups Links |
Reply by ●February 13, 20042004-02-13
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Here's how I see it...if you are thinking about creating your own
CAN protocol you need to consider the following (first, study as many of the other CAN protocols as you CAN) You are going to have to consider three areas 1) How to define the CAN ID's to transfer data to and from your node 2) How are you going to define the packet data to transfer data in a standardized method 3) How are you going to handle the flow of data with respect to nodes communicating on their own, in response to polls and in response to emergency or unexpected events. For 1) this can be as simple as each node getting a node number and that is used in its ID. Any messages sent to that node are sent to that ID. The problem is that if you have more than one node sending to the same node, you'll have a problem with the ID's being the same and they might get sent at the same instant. So, the easiest is to add the senders ID to the ID so that the ID is based on some number of bits making up the sender address and some number of bits making up the receiver ID. The receiver uses its filters to except any message that is addressed to it without regard to the senders address. Now, you could also take this one step further and instead of just sending to and from the node in general, you could add devices within the node. You could use the CAN ID to encode a 7 bit sender node address, a 7 bit sender device, a 7 bit receiver node address and a 7 bit receiver device. (assuming 29 bit ID is used) This would give your network 128 nodes with each node having 128 unique devices, being whatever you want, motors, switches, outputs, etc etc. Keep in mind this is just one method and other protocols like CANOpen and J1939 have different methods. Also, you can reserve the node address zero/ device address zero for anybody that wants to broadcast data to everybody in general. This means if you have a switch that changes state and you don't know who on the network cares about it, you broadcast it to mynode/mydevice/zero/zero and it is up to the reciever to know to look for that node/device packet. 2) Ok, so now you can send data to and from any node on the network, now you must define what the data looks like. For a simple protocol, you can just define that the first byte of the protocol is a command byte and that this defines how the rest of the data is organized. For example, define the command value of one to mean "send my your value" and two to be "Here is my value". You could leave it up to the receiver to know that a particular node/device will be sending data in a particular format, with regards to the rest of the packet or you could define a second byte to be a data type identifier that defines the following data to be 1 bit, 1 byte, 2 bytes, 4 byte floating point etc. If you are sending data that spans more than one packet, than you need to define a command for multipacket data and a byte or two to define the index number of the packet currently being sent. With one command byte, a two byte index, this leaves 5 data bytes*0xFFFF(index) for 320K of data. Again, this is a simple method for a simple protocol. 3) OK, this is turning into a novel...actually, I think I'll leave it here for now, I've covered some of point three already anyway. Steve Steven D. Letkeman BSc. President - Zanthic Technologies Inc. 403-526-8318 www.zanthic.com Embedded micro-controllers and CAN interfaces www.brightan.com Automated lighting systems ----- Original Message ----- From: "hc08jb8" <> To: <> Sent: Thursday, February 12, 2004 8:52 PM Subject: [68HC12] HCS12 and CAN Bus > Hi Folks > > I am trying to use CAN bus as a communication link in a project. I > have a CAN 'Master' connected to the PC and several CAN 'Nodes'. > These nodes are based on Motorola HCS12C32 MCU with CAN. I have got > the communication working however I find the default maximum transfer > of 8 bytes per transaction somewhat limiting. > > When searching for higher level protocol layers, most of them seem to > be quite expensive or complex. I would like to find out if there is > any simple low cost higher level layer that could handle messages and > so forth greater than 8 bytes? > > Another question is, the MCU i use has a Identifier Acceptance > Register and a Identifier Mask Register, I am a bit confused as to > which should I set if I need to filter only one ID, say for example: > accept only messages with ID of 0x105. > > Regds > Jay > > > --------------------To learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu > o learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu > > Yahoo! Groups Links > |
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Reply by ●February 13, 20042004-02-13
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Hi Steve, > 3) OK, this is turning into a novel...actually, I think I'll leave it here > for now, I've covered some of point three already anyway. ..and you have covered it VERY WELL! Thanks, Bob Furber __________________________________________________________ Connect your micro to the internet the easy way www.microcommander.com Microcontroller with an obscenity of I/O & features ..in a small footprint www.steroidmicros.com __________________________________________________________ |
Reply by ●February 13, 20042004-02-13
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--- In , "Steve Letkeman" <hc12list@z...> wrote: > Here's how I see it...if you are thinking about creating your own CAN > protocol you need to consider the following (first, study as many of the > other CAN protocols as you CAN) You are opening a CAN of worms here... |
Reply by ●February 13, 20042004-02-13
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thanks Bob, most of what I was describing comes from the protocol I designed for the HC12+CAN based lighting system I've been developing. The protocol is designed to be used for lighting commands plus the ability to add other, yet to be defined, equipment (alarm systems, temp sensors, weather station, music control, etc etc) without getting so complex you need months to understand the protocol and a megabyte to implement. The newest version allows firmware to be downloaded across the CAN bus as well. Steve Steven D. Letkeman BSc. President - Zanthic Technologies Inc. 403-526-8318 www.zanthic.com Embedded micro-controllers and CAN interfaces www.brightan.com Automated lighting systems ----- Original Message ----- From: "Bob Furber" <> To: <> Sent: Friday, February 13, 2004 10:10 AM Subject: RE: [68HC12] HCS12 and CAN Bus > Hi Steve, > > > 3) OK, this is turning into a novel...actually, I think I'll leave it here > > for now, I've covered some of point three already anyway. > > ..and you have covered it VERY WELL! > > Thanks, > > Bob Furber |
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Reply by ●February 13, 20042004-02-13
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Hi Steve > ..most of what I was describing comes from the > protocol I designed for the HC12+CAN based lighting > system I've been developing. > > www.brightan.com Automated lighting systems Impressive! Your Yacht? What do you use as the USB4CAN device? Did you roll this yourself? Or, is it an off-the-shelf item? Bfn, Bob Furber __________________________________________________________ Connect your micro to the internet the easy way www.microcommander.com Microcontroller with an obscenity of I/O & features ..in a small footprint www.steroidmicros.com __________________________________________________________ |
Reply by ●February 13, 20042004-02-13
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Ya, that's my $15 mil yacht I earned doing embedded processor work, doesn't everyone have one? The CAN-4-USB is an interface that I've designed and have been selling for a number of years now. http://www.zanthic.com/can4usb.htm (thanks for asking and sorry for the blatant plug) S > Hi Steve > > > ..most of what I was describing comes from the > > protocol I designed for the HC12+CAN based lighting > > system I've been developing. > > > > www.brightan.com Automated lighting systems > > Impressive! > > Your Yacht? > > What do you use as the USB4CAN device? Did you roll this yourself? Or, is it > an off-the-shelf item? > > Bfn, > > Bob Furber > > __________________________________________________________ > > Connect your micro to the internet the easy way > www.microcommander.com > > Microcontroller with an obscenity of I/O & features > ..in a small footprint www.steroidmicros.com > __________________________________________________________ > > --------------------To learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu > o learn more about Motorola Microcontrollers, please visit > http://www.motorola.com/mcu > > Yahoo! Groups Links |
