You mention that you have a crystal and its two caps and a 4 volt power source for your AT89LS52 circuit. However you did not mention other circuit connections. There is a minimum set of additional considerations for connection of this part into the simplest test circuit that must be taken care of if you expect the chip to operate properly.

Did you......

1) Take care to tie both power pins of the microcontroller to the power supply....Vcc to +4V and GND to the return side of the supply? It is also highly advisable that you provide for some supply bypass capacitance directly across the power pins of the chip. A good starting choice would be a 0.1 uF monolythic ceramic capacitor.

2) Did you provide for a means to supply a proper RESET signal to the microcontroller at the RST pin? A reset supervisor chip is recommended for this purpose. This processor may try to output a pulse on the RST pin if the internal watch dog timer is left enabled and your code lets it timeout. If this is likely to happen in your circuit AND if you use a reset supervisor that has an active output you must then include a resistor of about 2.2K to 4.7K ohms between the reset chip output and the RST pin of the microcontroller.

3) Since it sounds like you are trying to use the onboard FLASH memory to hold your program did you take care to strap the /EA pin to Vcc so that the chip would be sure to use the internal memory for the program fetches?

4) Did you use an oscilloscope to verify that the chip is working at all? You should by default see some pulsing on the ALE pin unless you set the fuse bit that disables this feature.

5) Also with an oscilloscope you should be able to verify that the crystal oscillator is running. Do you see a 11.0592 MHz signal on the XTAL2 pin?

6) Clearly you have used some means to write your program into the FLASH memory. Did you read the program back out in a VERIFY mode to check that it had been programmed properly?

7) This chip has a normally recommended VCC of up to 4.0 volts. This is a kind of unique voltage rating being that most other chips of the various 8051/52 types are nominally used at 5 volts or 3.3 volts. Have you carefully checked your power supply to see that it is indeed 4.0 volts? An oscilloscope can also be used to check that this voltage is a nice clean DC level without excess noise or ripple. If your supply had 1 or 2 volts of ripple on it there is little chance that the microcontroller would operate correctly.

8) The microcontroller will require about 25 mA of operating current from the power supply in order to operate correctly. Now while that is not really a lot of current for a typical power source there are connection mistakes that could limit the amount of current available to the microcontroller. Have you checked that your supply can provide the necessary 25 mA at the 4 volts? This is easy to check by removing the processor from its socket and then using a temporary 100 ohm to 150 ohm resistor across the VCC to GND connections to see that the 4 volts stays at 4 volts as the resistor is connected.

Good Luck
Michael Karas