Asok Sankar Rudra wrote:
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1)Why use AT89S8252,why not AT89C52 since for reasons of availability you decided use external RAMs so the FLASH is not going to be used anyway?
2)I ground External Enable /EA external memory access
i.e Address 0000 starts from 0000 of device getting Y0
from '138. In this mode P0 time-multiplexes lower address and data. This lower addresed is latched out and fed as input to external RAMs,which get data input straight from P0. Thus for external memory access P0 and P2 (generating A8 to A15) are required.

Asok, please note that the external RAM is DATA, not CODE (RD and WR, not PSEN), so internal code flash will still be used. As a result, /EA will still need to be tied high.

Dennis