Is the same DD command appropriate for writing EMMC and SD cards

[wpeckham]

I have written several SD cards and they all work from software on other machines. I have written images from SD card to emmc and had it work. Now I want to back up my emmc to an SD card and be able to boot from it.  Can I have DD read from the emmc device and write to the SD device and get that?

UPDATE:  I found a spare SD card, dropped it in the clot, and ran
sudo dd if=/dev/mmcblk2 of=/dev/mmcblk1 bs=1M status=progress
where mmcblk2 is my emmc
and mmcblk1 is my sd card

It took a good while, but finished without error.  Rebooting the PBP brought me into the same session, settings, and everything as if I had booted to emmd without the card, except that the root mount point was on mmcblk1 now.

This is perfect.  As easy as that I have a card that is a clone of my usual boot to use as a backup card in case of issues, and from which to rewrite the emmc at need. 
UPDATE: 2021-11-13 I have now had it succeed once, and fail once.  (To the same SD card from the same EMMC!) so the lesson is that it CAN work but you might want another solution available: just in case.