Gabriel,

Okay, I was already under the impression that this wasn't all. If you want people to assess your code, at least make it more clear where the parts are located, because posting fragments without proper comments about what isn't there will prohibit people on this board to take a serious look at it.
Please use English for your comments, because that will make it easier on occasions like this for other people to understand what you are trying to do.

CLR comes in only two flavors:

clr a

which clears the accu, and

clr bitaddress

which clears a bit.

If you say

clr STP

it will be taken as clear the bit at bit address STP. There is no CLR instruction for clearing a complete byte. If STP is a byte, then you will have to use

mov STP,#0x00

or something. For instance,

clr a
mov STP,a

would work too.

Hans

ps. a timer interrupt every 100us is a terrible strain on an 8051 type CPU!