programming Atmel AT89S52

[Peter]

Hi,

I'm trying to build a small programmer for an AT89S52 µC,
by using a programmed AT89C2051 as a serial to parallel converter
and an application on my computer to create the ISP signal.

I didn't have any problems sending the "Programming Enable" command to
the controller and also got the proper output form the 89S52.
Programming the rom also seems to work, but the controller doesn't
behave as expected after setting RST to low.
I created a small test program, that should just output #10101010b on
all Ports, but every pin is just set to high.

Here's the asm code I use for testing:

#include "8051equ.inc"

begin:
mov P0, #10101010b
mov P1, #10101010b
mov P2, #10101010b
mov P3, #10101010b
ajmp begin
.end

Any ideas why I don't get the expected output on the ports?

Thanks in advance
Pete