Sometimes you need to do something yourself... That POKE &HF3B1,value only works with the top value lines. to scroll the lower part, you can do 2 things:
- copy the lower part to RAM from the next line and copy it back with 80 spaces added to it
- copy the upper part to RAM, let the BIOS do its scrolling work and restore the upper part
I'd suggest doing the first as the second looks pretty ugly.
I did something like this about 10 years ago when I was investigating MIDI... I wrote a split screen chat to do something useful with the MIDI routines that came up during those investigations. Though the lower part was done completely in BASIC back then 
I just checked the BASIC file. It used a VT-52 code to scroll the lower part: ESC+J
Well, that also doesnt work for the lower part of the screen.
i tried everything but everytime its only the upperpart of the screen that scrolls.
i just can't seem to have the lower part do anything.. i can only vpoke to it. but vpoking code 27+asc(M or L) is quite useless 
though its an interesting site. didnt know using escapes was possible like this
Ehm, VPOKEing and escape codes don't match. You'll have to use plain old LOCATE and PRINT
scroll bottom half of the screen one line up:
LOCATE 1,13: PRINT CHR$(27)+"M";
Scroll top part (or actually, scroll complete screen up, and then bottom part back down):
LOCATE 1,1: PRINT CHR$(27)+"M";: LOCATE 1,13: PRINT CHR$(27)+"L"
(I can't remember if top left of the screen is 1,1 or 0,0 for LOCATE. Change accrodingly...)
after checking with the VT-52 docs... I used that ESC+J to clear the screen from the location I provided... it was really too long ago when I seen the program last
I also saw a ESC+M in the program... that indeed I used to scroll the bottom part... it deletes a line...
I don't think what you want to do can be done in BASIC. Fortunately though, it's pretty easy in ASM. (Everything is 
) Anyhoo, see if this little piece of code does the trick... I haven't tested it, but it should probably do the trick. Assemble with your favorite assembler and change the address if needed. You can still use LOCATE and PRINT in BASIC, but you can also use the function provided here while poking the X/Y coordinates to the vram_address thingy as shown. Hope it helps...
Screen_Width: EQU 80 Upper_Screen: EQU Screen_Width*0 Lower_Screen: EQU Screen_Width*12 ORG $C000 JP Initialize ; DEFUSR=&HC000: A=USR(0) JP Print_Text ; DEFUSR=&HC003: T$="Hi!": A=USR(T$) JP Scroll_Upper ; DEFUSR=&HC006: A=USR(0) JP Scroll_Lower ; DEFUSR=&HC009: A=USR(0) VramAddress: DW $0000 ; POKE &HC00C, (Y*Screen_Width)+X Initialize: LD HL,0+Screen_Width*11 LD DE,1+Screen_Width*11 LD BC,Screen_Width-1 LD (HL),$20 LDIR XOR A CALL $005F JP $00CC Print_Text: CP $03 ; DEFUSR Arg is string RET NZ LD A,(DE) ; Length of String INC DE LD C,A LD A,(DE) ; Low Byte Address INC DE LD L,A LD A,(DE) ; High Byte Address LD H,A LD B,0 LD DE,(VramAddress) ; VRAM Address JP $005C Scroll_Upper: LD HL,Upper_Screen+Screen_Width LD DE,Screen_Buffer LD BC,11*Screen_Width CALL $0059 LD HL,Screen_Buffer LD DE,Upper_Screen LD BC,12*Screen_Width JP $005C Scroll_Lower: LD HL,Lower_Screen+Screen_Width LD DE,Screen_Buffer LD BC,11*Screen_Width CALL $0059 LD HL,Screen_Buffer LD DE,Lower_Screen LD BC,12*Screen_Width JP $005C Screen_Buffer: DS Screen_Width*12
You're welcome? 