I'm reading some frames from the infotainment system, and I get multiple frames that forms a "package" (let's call it that) which forms a text. Each frame sent by the radio unit is received by a display module that sends back a confirmation frame (like a acknowledgement) with the same data, except for the last frame of the package sent by the radio, on which the confirmation frame is different from the rest with one bit. Tested for a long time on multiple messages.
Now, in order to remove the display, I need to know how long (how many frames) the package is, to use it in my application, but without that different acknowledgement frame sent by the display module, I am unable to continue my project.
My question is, how does the display module knows how many frames does it need to receive? Is it possible to be in one of the bits on the first frame received (I've tried checking, but none of the bits have a pattern related to the package's number of frames length)? Is it something else? I know about the acknowledgement bit on the frame, but that is just for checking if any device received that frame (there are about 6 modules on that CAN network, so that's why I believe the display sends confirmation frames).
I am a begginer in CAN, so any useful information is welcomed.
So it seems this kind of package, which consist of more than 7 bytes of data, uses the ISO 15765-2 protocol, that specify in the second byte of the first frame how many bytes do the package contains.