[Gmecm] j1850 and/or 68hc58 experience?

[Steve Ravet]

That's a good idea (the ELM device).  I took a closer look at the
firmware and I think there may be some problems in there, I should post
it on the twiki so you-all can eyeball it.

--steve

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Darren Freed
> Sent: Tuesday, May 08, 2007 12:28 PM
> To: gmecm at diy-efi.org
> Subject: Re: [Gmecm] j1850 and/or 68hc58 experience?
> 
> Steve,
> 
> The other thing you may want to consider is connecting an 
> ELM-based device on the Class 2 bus so that you can see what 
> you really _should_ be expecting to see.  I would think that 
> would take some of the uncertainty out of it.
> 
> FWIW, the receive msg doesn't make any sense to me either.  
> You really should see a response to the 'shut up' command 
> (mode $28).  That mode #3c request (VIN) has worked for me, 
> using the an AVT device.
> 
> Darren
> 
> 
> On 5/4/07, Steve Ravet <Steve.Ravet at arm.com> wrote:
> >
> > Some of you may recall that I'm working on a cable that 
> allows you to 
> > connect a PC to a GM OBD2 computer via USB.  I've made some 
> progress, 
> > I'm able to send the "shut up" message to the PCM to get it to stop 
> > broadcasting messages, but I can't read data back from the 
> DLC.  I'm 
> > using the hc58 in serial mode and have some questions about 
> that:  Do 
> > the status bytes you get back while transmitting a message mean 
> > anything?  I can't make sense out of what I get back from the DLC 
> > while transmitting a message.  And after transmitting a 
> message, for 
> > example requesting the VIN, I don't get any response.  On 
> the scope I 
> > can see the broadcast messages the PCM sends out but I 
> never see any 
> > bytes in the receive FIFO.  Here's a trace of the VIN request:
> >
> >
> >        data    command
> >        0x6c    0x14
> >        0x10    0x4
> >        0xf0    0x4
> >        0x3c    0x4
> >
> >        status   receive
> >        0x00,    0x00  (receive and send FIFOs empty)
> >        0x7b,    0x00  (receive FIFO full, end of frame not 
> seen, link
> > idle, link fault, send FIFO full)
> >        0x01,    0x00  (receive FIFO empty, send FIFO has data)
> >        0x18,    0x12  (receive FIFO empty, link idle, link fault)
> >
> >        data    command
> >        0x1    0xc
> >        0x0    0x0
> >        0x0    0x0
> >        0x0    0x0
> >
> >        status   receive
> >        0x00,    0x00
> >        0x7b,    0x00
> >        0x01,    0x00
> >        0x18,    0x12
> >
> > The transmit message is 6c 10 f0 3c 01, which requests the 
> VIN.  The 
> > status bytes don't make any sense to me, two of the status bytes 
> > report a link fault, which means the J1850 bus is shorted 
> to ground.  
> > You can't clear this status bit except by resetting the DLC 
> which I'm not doing.
> > Plus the FIFOs going from empty to full and back to empty 
> doesn't make 
> > sense, the FIFO is 12 bytes deep.
> >
> > --steve
> >
> > -------------------
> > Steve Ravet
> > ARM
> > steve.ravet at arm.com
> >
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