Hi Bert,

I found in AT89C51.PDF from Atmel (page 4-31)that:
"If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode."

I haven't looked at your specific device documentation though. I hope this helps.