Recessive state is when the bus is idle meaning no devices are transmitting messages. All devices on the CAN bus monitor the state of the bus and will only transmit if they detect a recessive state. This is to prevent data collisions from more than one device transmitting at the same time. When a device begins a transmission it sets the bus state to dominant which prevents other devices from transmitting.
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M939 CTIS Reprogram, Anybody Done It?
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therooster2001
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Cool, thanks. SO it looks like its CAN, but nothing is being transmitted. I fear that the flash is not supporting CAN. Unless we can figure out anything else, this might be a bust...
therooster2001
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Well normal CAN should speak up without being asked, but I guess it's possible. No Dana documentation has ever said how it communicates on either protocol, or even if it will, it's just a hunch based off the pin outs. I'll keep digging. And it might be call Dana to see if someone way back might know or give us more info...
therooster2001
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Both good basic websites on CAN communication and specs.
https://barrgroup.com/Embedded-Systems/How-To/Introduction-SAE-J1939
https://www.kvaser.com/about-can/higher-layer-protocols/j1939-introduction/
They reference a broadcast network. I'll check to see if I'm listening on the CAN shield at 250k or 500k, I seem to remember 125k in some code, but they are jumbling together in my head.
If nothing else, I am getting pretty smart if I were to have a functional J1708 / J1939 network to analyze.
https://barrgroup.com/Embedded-Systems/How-To/Introduction-SAE-J1939
https://www.kvaser.com/about-can/higher-layer-protocols/j1939-introduction/
They reference a broadcast network. I'll check to see if I'm listening on the CAN shield at 250k or 500k, I seem to remember 125k in some code, but they are jumbling together in my head.
If nothing else, I am getting pretty smart if I were to have a functional J1708 / J1939 network to analyze.
ramdough
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I am just glad that there are people out there like you who work hard to figure this stuff out.
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On the last waveform photo you uploaded I'm wondering if the places where the signals go high & low momentarily are when data transmissions are occuring. Have you tried adjusting the horizontal axis knob to zero in on these? Also, I took a look at your scope manual and it talks about a SGL(single sweep) button. This function may help you catch a data transmission before it quickly disappears.
therooster2001
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Yup, my CAN board and the RS485 both have those resistors to properly terminate the bus.
Would a resistor also be needed on the end near the CTIS module? And is the resistor on the can board 120ohm? The reason I ask is I have read some boards have a 60ohm resistor to try and accomplish simulating the two 120ohm resistors and this doesn't always work properly.
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therooster2001
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Hmm, Im not sure now. I always thought no, but I guess I should draw it out. Got a long plane ride to think it over. I think 74M was going to try that too, hey, where did he go with is one. 
74M35A2
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That is next step. Waiting for warmer/dry weather.Hmm, Im not sure now. I always thought no, but I guess I should draw it out. Got a long plane ride to think it over. I think 74M was going to try that too, hey, where did he go with is one.
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Bump for stellaevil
Stellaevil
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What is the ECU Part number?676422 and 676603 are the two possible choices that will communicate with a laptop. Not sure if the 422 has the CAN chip but 603 does for sure. What COM box are you using to connect? and is the box powered up properly. When using a USB com box sometimes I have to try all the ports on the computer. The harness will not work on the CAN bus without a 60 ohm resister tied between Can Hi and Can lo.
I should be able to help you get it working.
I should be able to help you get it working.
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Stellaevil
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What is the ECU Part number?676422 and 676603 are the two possible choices that will communicate with a laptop. Not sure if the 422 has the CAN chip but 603 does for sure. What COM box are you using to connect? and is the box powered up properly. When using a USB com box sometimes I have to try all the ports on the computer. The harness will not work on the CAN bus without a 60 ohm resister tied between Can Hi and Can lo.
I should be able to help you get it working. There are good wiring diagrams showing the communication connections.
Dana has released an updated CTIS troubleshooting manual.
AXTS-0015 http://media.spicerparts.com/media
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74M35A2
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Good response using data, thanks. I have not checked my module part number, nor tried the CAN bus termination resistor yet. I will at the beginning of this summer. The comm unit is the one recommended by DANA, which is also on their approved comm module list, please check my earlier posts, as I spell it out there.
therooster2001
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Nothing new in that manual unfortunately. 422 testing. Tried with termination with a prebuilt CAN Arduino, an Rs485 with code from Arduino, and a scope (no terminator) and tried both J1708 and J1939. I will try one last termination with 120ohm and a scope, but the bus is QUIET, all in recessive mode. I think the flash is still not diagnostic capable. Would love to be proven wrong there.
Reading the other thread, can you verify the flash enables either CAN or J1708 diagnostics on the 422? Thanks for your help. If a phone call is better, I'm in.
Reading the other thread, can you verify the flash enables either CAN or J1708 diagnostics on the 422? Thanks for your help. If a phone call is better, I'm in.
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Stellaevil
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The ECU part number will be very important as the older ECU's do not have com software imbeded. I will make sure the newer ECU have the com active in the software.
Stellaevil
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Both ECUs listed above have 1708 and CAN communication capability. The original green ECU has no com capability and all the unused pins are internally traced to ground and could damage you com box. The DDT tool is pretty reliable over the J1708 connection. The ECU software may not broadcast on the link until the tool has synced with it. so with a scope you may not see anything from the ECU without the combox connected and the DDT tool running. The tool will poke the CTIS for a few seconds and then time out "no connection" If the com box is powered by the computer you should only need the 1708 +- lines connected. There is no resistance on that bus needed like the CAN bus.
74M35A2
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This is the result I am getting so far.
I see all the pins are populated in the connector, but not in the vehicle harness, so I made an inline harness that adds them. So far, the diag software and comm adapter try for a few bytes, then no response and gives up, saying no comm.
I hear all the xMTV CTIS modules can communicate, but they are 12v? Also their button sequence is opposite the M939a2 layout, I think.
I see all the pins are populated in the connector, but not in the vehicle harness, so I made an inline harness that adds them. So far, the diag software and comm adapter try for a few bytes, then no response and gives up, saying no comm.
I hear all the xMTV CTIS modules can communicate, but they are 12v? Also their button sequence is opposite the M939a2 layout, I think.