The simple setup of counting registers [digit1..4] and the INC on every loop creates an overflow to indexed search because the table consists of just 16 entries. This can be considered on the [segdiplay] part of the code. Actually it is not about a moving display but for a specific rolling counter using hex digits 0..9 and A..F

The part of [segdisplay] should be corrected to use only the lower nibble since the lookup table has only 16 entries.

segdisplay:
         mov dptr,#lookup              
         ANL A,#0x0F                     ; ADDED to clear upper nibble before used to index
         movc a,@a+dptr
         cpl a
         mov p1,a
         call delay1ms
         mov p1,#0ffh
         ret

 

Also the table entries for seven segment display decoding is partially correct.
This file may be trivial but can help a lot anyone interested to 7segment display decoding to port pins.

http://www.8052.com/users/angelis/sevensegment.xls



K.L.Angelis