"p0 port reads data from diffrenet chips"
these chips use current too.

Remember the recified DC will be close to root 2 times the AC woltage from transformer so the poor little 7805 is probably dropping more than 10 V which at 500mA equates to 5 W.
Why your transformer gets hot, I dunno. Peter suggested that you use 80C51, If you are actually using an old HMOS chip, throw it out.

Erik