Has anyone ever seen this problem?

I have a BASIC-52 circuit with a 32K SRAM (Toshiba 65526) addressed from 0-7FFFH and a 32K NVRAM (DS1225AD) addressed starting at 8000H. I'm assuming the wiring is correct; there may be an error.

If I type the following at the prompt,

> XBY(8000H)=0

and then,

> PH0.CBY(8000H)

BASIC-52 returns 0.

However, if I write the following program:

10 FOR I=8000H to 9FFFH
20 XBY(I)=0
30 IF CBY(I) <> 0 GOTO 50
40 NEXT I
50 PRINT I," ITERATION(S) COMPLETED--ERROR" : END

The program ends before completeing one iteration.

What's going on here?

Dan