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Understanding communicatins in general, SCP and CAN bus (Vince)

CowboyBilly9Mile

Charter Member
7,118
442
USA
I've got a project I'm working on (EATC) and despite reading and researching in hope of finding an answer(s?), I've met a road block. So maybe if I stick to simple questions and in hopefully a general sense, maybe I can get somewhere. Here we go.

a) On pre CAN bus Ford vehicles, was the PCM programmed to specifically provide data to only factory installed options or is that data always available on the SCP bus and it was up to the module to have the logic built into it to access and use it?

b) When Ford migrated a vehicles electronics from pre-CAN bus to include the CAN bus, did some of the data that was once made available on the SCP bus get transferred over to the CAN bus and now, the SCP wouldn't have it?

c) Has Ford changed the rate of data transfer (baud rate) on the SCP bus over the years and if they did......and I think this may be a long shot but.....is the data transferred on the new SCP version (if this is true) backwards compatible, meaning they only provided for new and left previous operations and functions alone? I realize SCP has two speeds, but am still curious.

EDIT d) On Ford EATC head units of the SCP only vintage (96-03ish, depending on the vehicle), do they update the outside temp data more frequently when receiving data from the bus or is the no data connection default going to be the fastest?

*I ask all this because, as I prep for and EATC mod and as I test functionality, I have strong reason to suspect that the EATC head unit is not communication with the PCM. A head unit from pre CAN bus days but is wired to a vehicle in year one of CAN bus inception, yet there is the SCP bus pins (2 and 10) staring right at me in the OBDII port. Temp updates going down are frequent, bus or no bus, running vehicle or not, but temp updates for increasing temp, bus/no bus, running driving vehicle or not are unreasonable slow. Like, 85* day, and it goes from 72 to 75* in 1hour, 20 minutes.
 
Last edited:

blacksnapon

Moderator
Staff member
Essentialy, think of it like this... instead of having numerous wires from each module to the pcm, just use 2. It's like a string of Christmas lights. Generally, you have high speed CAN and Medium speed CAN. Lately, theres also the LIN network. The progression of the systems get faster and more complex. Systems pre-CAN are now on the CAN networks. Pre-CAN components generally are not compatible with CAN-BUS systems.
 

CowboyBilly9Mile

Charter Member
7,118
442
USA
I do understand the concept of the bus, but I am wondering if a pre CAN module designed to communicate with the PCM via SCP will communicate with a system that has, as seen by the pinout on the OBDII port, both SCP and CAN, and said communication will be by SCP bus.
 

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