topic Re: MPC56xxx Byte Ordering and Bit Numbering in MPC5xxx

MPC56xxx Byte Ordering and Bit Numbering

tgc-yilmaz — Fri, 15 Dec 2023 08:09:50 GMT

Hello,

MPC56xxx is used and Byte Ordering "Big Endian" is selected. At this point, there is confusion regarding bit ordering.

The Big Endian byte order is expected to be in the following format, but when the datasheet is examined, it is seen that it is as in the image below.

In the CW IDE, it was observed that the bits were positioned as expected. In this regard, can you provide detailed information about byte and bit ordering?

Thanks.

Re: MPC56xxx Byte Ordering and Bit Numbering

lukaszadrapa — Mon, 18 Dec 2023 06:50:03 GMT

Hi @tgc-yilmaz

MPC56xx are Big Endian only devices. Little Endian cannot be configured/used ever.

The only catch here is that our reference manuals use bit numbering 0-31, not 31-0. That's due to some historical reasons.

Regards,

Lukas

Re: MPC56xxx Byte Ordering and Bit Numbering

tgc-yilmaz — Mon, 18 Dec 2023 07:18:15 GMT

Hello,

First of all, thank you for the answer. In this case, can I accept the general format for bit numbering for big endian, regardless of the reference manual?

Big Endian Order:

Byte 0	Byte 1	Byte 2	Byte 3
bits 31-25	bits 24-16	bits 15-8	bits 7-0

Thanks.

Re: MPC56xxx Byte Ordering and Bit Numbering

lukaszadrapa — Tue, 19 Dec 2023 08:45:22 GMT

Yes, in general, that's correct.

Regards,

Lukas