First of all, he has no internal ROM, since his is a masked-rom part. Secondly, I doubt that Basic-52 could write its own EPROM, unless it had the then-popular and very much necessary 25-volt supply available with enough current (about 50 mA) to do the job. The +5 supply to an EPROM had to be heftier than just what comes out of a logic device, too, else you'd just see a reflection of the nCE to the EPROM. IIRC, BASIC-52 assumed it ran in an environment with which it used a port pin to select between EPROM and RAM, and it could write to an external RAM in code space from its internal EPROM. Without that little feature, it essentially didn't work at all.

I'm convinced that his main problem will come from the circuit with which he manipulates the Xtal1 and Xtal2 pins. On some devices, Xtal2 is an output, on others it is an input anticipating the complement of the Xtal1, while on others yet, it wants to be grounded. Check the Intel datasheets for details.

I'm thinking that this O/P is playing with a part he happens to have and that's why he's using external memory. If that's the case, he has a number of options, starting, actually, with BBRAM, e.g. the Maxim/Dallas DS1230Y. If he plugs one of those into the code space, with nWR jumpered to pin 27, he'll have a working system, assuming he's got everything else right. He will, absolutely, have to have the "right" crystal oscillator driving his MCU so his serial port will function properly. He should be sure he has proper support in firmware for whichever frequency he chooses.

I'd steer him onto ULTRAMON51 as an intermediate development tool. It's downloadable and affords lost of support.

RE