We've wandered off the O/P's topic completely, now, Erik. I appreciate that there's a use for SPI, as it's quite popular, but we're supposed to be focused on a byte-wide problem, i.e. Munaza Yousuf chose 8-bit components for a reason as yet unknown, and a 9-bit protocol would work only with considerable firmware overhead. That would render it a poor choice for this hardware. Likewise, the mode-0 serial channel wouldn't do any better.

The "biblical" i8051 doesn't support SPI, though, does it?

If you have to use SPI in order to effect communication between your devices, you've got no choice. If you want efficient communication, generally speaking, you won't be using any sort of protocol that wastes two or more bits of bandwidth per byte, though.

If the (auto or any other) industry uses a protocol that's wasteful, that doesn't surprise me. Not all their engineers are complete blockheads, but enough of them, particularly those that have crept into senior engineering management, are. They don't care if they waste bandwidth. They don't care if they waste fuel. They don't care if they waste their stockholders' retirement resources. They just want to play golf and slap one another on the back.

RE