"Yes, but it's a hack. Standard issue '51/'52 architecture separates the memories - MOVX is for R/W on data, MOVC for Read on code - or at least that's what the original designer intention was - and anything that allows MOVX to access code memory (or any code memory write operation for that matter) is beyond the basic specs "

No it is NOT a hack. When I said,

"Both PSEN and !RD needed for accessing external code memory WITH a movx instruction."

I had based it on Fig.16 on page 13 of the following PDF.

http://www.semiconductors.philips.com/acrobat/v...ARCH_1.pdf

Hope I am clear now....

Raghu