There are very few differences between a 16F88 and 16F628...

Firstly addd this to the defines at the start of your program...

cmcon equ 0x1F

Then also at the start of your program where the port tris registers are being defined add...

movlw 0x07
movwf cmcon

Look in the Datasheet (Section 9.0 & 9.1) to see what I have done.