hi,

However, if I change MOV DPTR,#STRING1 in "DSPSTRING" section to mov DPL,#00h and mov DPH,#01h along with STRING1 to .ORG 0100h,

Generally, for such purposes there is no reason to load DPH and DPL separately. Anyway if you have the reason so I may suggest you to replace it with such way:

MOV DPL,#LOW(STRING1)
MOV DPH,#HIGH(STRING1)

This way you need not with absolute address calculations yourself; all will be done with compiler (here: Keil).

Regards,
Oleg