Binary values in hexidecimal notation written directly to video memory
This is a very nice routine that totally succeeds in using a direction flag set to 1. I've seen others fail at this.

Some observations:


731  BF200A            mov     di,0xa20      DI = 5DC 



It's not clear what you mean with "DI = 5DC"


  One thing I had considered here is adding 444H to DI instead, which in effect does exactly the same and then the left column would stay relative if the word at 709H was changed.


I would definitely choose adding 444h to DI in such a specially crafted routine. Relative addressing is so much more flexible to work with.


6F6  B82D0F            mov     ax, 0xf2d
6F9  66AB              stosd                  Write bright white hyphen



This is the only place where your code conceivably could fail. You store the dword from EAX without making sure the high word has any meaningful content. If the high word is empty you're in the clear, if not the screen will get disrupted.
Since modern BIOSes do use 32-bit registers, you can't be sure...

The shortest way to 'correct' this is:

mov     ax, 0x0F2D
stosw
dec     di
dec     di