Does the C7 have a CAN Buss?
Thread Starter
Racer
Joined: Jan 2011
Posts: 299
Likes: 2
From: Canyon Lake TX
Does the C7 have a CAN Buss?
I was wondering if the C7 computer puts out it's data on a CAN (Control Area Network) buss. If so, Racelogic has a device to tap into the data stream, and output very accurate information for vehicle speed. Since the list of compatible vehicles includes many GM products, I would think the Corvette would use this efficient way of handling data. However, the Corvette is not listed in their compatibility chart.
Anyone know????????
Anyone know????????
Burning Brakes
Joined: Dec 2013
Posts: 1,051
Likes: 302
I was wondering if the C7 computer puts out it's data on a CAN (Control Area Network) buss. If so, Racelogic has a device to tap into the data stream, and output very accurate information for vehicle speed. Since the list of compatible vehicles includes many GM products, I would think the Corvette would use this efficient way of handling data. However, the Corvette is not listed in their compatibility chart.
Anyone know????????
Anyone know????????
http://www.betweentheaxles.com.au/co...hd-videos-4221
Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
I was wondering if the C7 computer puts out it's data on a CAN (Control Area Network) buss. If so, Racelogic has a device to tap into the data stream, and output very accurate information for vehicle speed. Since the list of compatible vehicles includes many GM products, I would think the Corvette would use this efficient way of handling data. However, the Corvette is not listed in their compatibility chart.
Anyone know????????
Anyone know????????
Thread Starter
Racer
Joined: Jan 2011
Posts: 299
Likes: 2
From: Canyon Lake TX
As in a previous thread, I am looking for an output to give me pulses when the vehicle is in motion. I have found a module by Racelogic that will tap into the CAB bus and has speed and RPM outputs. I'm just trying to get that signal. If I can tap into the CAN bus signal from the OBD II port, that would make life so much easier than tracing down a wire. The Racelogic rep in the US hasn't responded to my questions, and I have sent an email to the UK distributor. The UK site has several options that may work, including a model that hooks up to the OBD II port.
http://sailesmarketing.com/products/can-bus-interfaces/
I have until next April before I need this gizzmo in the Big Bend Open Road Race, but would like to get it up and running for some testing.
The software is just about ready for testing. I can do that on my C6. But a friend would like to have the system in his new C7 for next year's race.
Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
Yes, while we could never locate a proper VSS, etc. for you, the OBDII port should be able to read out that information in real-time via the CANBUS interface.
There is a limit on refresh rate, but if I remember correctly, it's around 50ms (20 updates/second) - more than fast enough for what you're wanting.
There is a limit on refresh rate, but if I remember correctly, it's around 50ms (20 updates/second) - more than fast enough for what you're wanting.
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
OBD II standards have speed in km/h in Mode 01 at PID address OC (in hex). It's supposed to return a byte (255), but have logged speeds way faster than that. So data bytes 1 and 2 must be being returned.
I can probably get to some testing this weekend. Also you can get faster than a PID every 50 ms updates.
I can probably get to some testing this weekend. Also you can get faster than a PID every 50 ms updates.
Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
OBD II standards have speed in km/h in Mode 01 at PID address OC (in hex). It's supposed to return a byte (255), but have logged speeds way faster than that. So data bytes 1 and 2 must be being returned.
I can probably get to some testing this weekend. Also you can get faster than a PID every 50 ms updates.
I can probably get to some testing this weekend. Also you can get faster than a PID every 50 ms updates.
OBDII is/was limited to 10,400bps - the rule used to be 18 I/O /s before CAN.
Last edited by Theta; Jul 16, 2014 at 11:30 PM.
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
It depends on how loaded the bus is... There is no fixed interval imposed.
EDIT - most scanners likely impose a limit to be safe...
EDIT - most scanners likely impose a limit to be safe...
Last edited by Skunkworks; Jul 16, 2014 at 11:42 PM.
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Tech Contributor
Joined: Jan 2006
Posts: 4,761
Likes: 240
From: Saint Louis MO
St. Jude Donor '14-'15
Looks like CANBus is limited to 1Mbit, so around 100 times faster than OBDII. 130bps is the round trip for a PID, so 80 round trips per second total would be the max for OBDII.
At 100 times faster, CANBus would allow 8000 round trips, so you're right - it's pretty much wide open up to the limit of the tool.
At 100 times faster, CANBus would allow 8000 round trips, so you're right - it's pretty much wide open up to the limit of the tool.
Melting Slicks
Joined: Apr 2005
Posts: 3,418
Likes: 1
From: Chicagoland Area IL
OBD II has multiple protocols at various speeds, it is still technically OBD II. CAN is 500 Kbit, others much slower, you have CAN, VPW, PWM, ISO and K-line all in one connector (different pins and usually only one network type present).
In most cases CAN bus is shared by multiple modules so depending on network load you’ll see limit imposed by other modules, because xx% of bandwidth is gone in normal operation.
To OP, Mode and PID address in hex. A standard packet is 8 bytes of data in length, not including overhead…
In most cases CAN bus is shared by multiple modules so depending on network load you’ll see limit imposed by other modules, because xx% of bandwidth is gone in normal operation.
To OP, Mode and PID address in hex. A standard packet is 8 bytes of data in length, not including overhead…
Thread Starter
Racer
Joined: Jan 2011
Posts: 299
Likes: 2
From: Canyon Lake TX
Theta, and Skunkworks,
You guys are way over my head. I'm more of s mechanical type, than an electronic/computer type.
Theta, on your C7 schematics, can you locate the PCM C2 Pin 50? My friend that is developing the software, tells me that this is the VSS signal. If so, where is the PCM located, and where would be the best place to tap into the wire from pin 50? (in the C6, it is circuit 817, green w/white wire, and I taped into it behind the radio)
I was able to find a module to convert the OBD speed signal to pulses, but my friend tells me it wouldn't be accurate enough the way it derived. I need it to be as precise as I can get it. In my C6, during the Big Bend Race, I was only off 52 ft in 59 miles. I was trying to stay in my lane as much as I could, since that is where I measured the course (Highway) to begin with. On Race Day, at 100+ I didn't have to stay in my lane, and after looking at the video, I didn't.
You guys are way over my head. I'm more of s mechanical type, than an electronic/computer type.
Theta, on your C7 schematics, can you locate the PCM C2 Pin 50? My friend that is developing the software, tells me that this is the VSS signal. If so, where is the PCM located, and where would be the best place to tap into the wire from pin 50? (in the C6, it is circuit 817, green w/white wire, and I taped into it behind the radio)
I was able to find a module to convert the OBD speed signal to pulses, but my friend tells me it wouldn't be accurate enough the way it derived. I need it to be as precise as I can get it. In my C6, during the Big Bend Race, I was only off 52 ft in 59 miles. I was trying to stay in my lane as much as I could, since that is where I measured the course (Highway) to begin with. On Race Day, at 100+ I didn't have to stay in my lane, and after looking at the video, I didn't.