how come BCD Decrement for #20hex become &25 in decimal?

[kartika]

i'm newbie in PLC, would u like to help me, plese..
i'm using an instruction MOV, for moving Hexadecimal data #0020 which is &32 in decimal,to memory D100, after that i'm decrementing(BCD decrement) the value of the memory D100,i'm confuse how come the result is &25(decimal)?
thank you for the attention

 

[jvdcande]

Decrementing BCD 20 results in BCD 19. If you convert from HEX 19 to decimal it becomes 25. Lesson: never mix your formatting unless you're absolutely certain what will be the outcome.

Kind regards,

 

[kartika]

thanks jean, its so help full
i understand, so if i got #30(hexadecimal) the result is #29 hex which is same with 41 in decimal, is it right?
#29 = 0010 1001
thank you very much

 

[jvdcande]

so if i got #30(hexadecimal) the result is #29 hex which is same with 41 in decimal, is it right?
#29 = 0010 1001

Yes, it is.

Kind regards,