Hi my friend,

Form point of my view If you are not interested in the speed of the program you can use an another method. First you convert the 16-bit BCD value to binary and then you can use the <subb> instruction in to do what you want.

Also, the result you must convert it back to packed BCD or unpacekd BCD.

I have these routines, namely
BIN to BCD and BCD to BIN

I am working on a KEYPAD and DISPLAY with 8051 and particularly with (89C51RD+). If you are doing the same thing feel free to contact me and I give you more details and some tricks in order to avoid the need of BIN to BCD routine.

my email: v_katsos@usa.net

Have a nice day,
Katsos vagelis