ASCII LSB-MSB logistic

[qtommer]

ASCII encoded bytes are mostly transmitted from LSB-MSB (LSB first) in various MCU UARTS.
Is there any reason why it goes from LSB-MSB? Any convention/logistic reason why this happens? Thanks!

 

[Nigel Goodwin]

They are ALWAYS sent the same way, things wouldn't work if they weren't.

Presumably the direction was specified in the original RS232 design, and has remained the same ever since - it really makes no difference which way you do it, as long as it's always the same.

 

[3v0]

Currently is is simply a convention. It could have been done both ways. The important thing is that everyone agrees so as not reverse the bit order.

To find why it was originally done one would have to find the first uart, or maybe even the first use of serialized data. Not sure how many decades back and what level of technology one would have to look into.

Heck it could go back to semaphore flag signaling, and at that level of technology it would also be strictly a convention too.

EDIT: RS232 is a somewhat modern technology. Prior to it teletypes were using current loop interfaces.

 

[Nigel Goodwin]

Currently is is simply a convention. It could have been done both ways. The important thing is that everyone agrees so as not reverse the bit order.

To find why it was originally done one would have to find the first uart or maybe even the first use of serialized data. Not sure how many decades back and what level of technology one would have to look into.

Heck it could go back to semaphore flag signaling, and at that level of technology it would also be strictly a convention too.

I would have thought back to teletypes etc. - there 'may' have been a mechanical reason for it originally?.

 

[3v0]

We were both thinking the same thing. I suspect no matter how far one goes back it will still be a simple convention. Even if you build the circuits with relays shifting left or right are equally hard.