The manual for ADuC841-2-3 mentioned the EWAIT SFR:
" External Memory Access
There is no support for external program memory access on the
parts. When accessing external RAM, the EWAIT register may
need to be programmed to give extra machine cycles to MOVX
commands. This is to account for differing external RAM access
SFR Address 9FH
Power-On Default 00H
Bit Addressable No
This special function register (SFR) is programmed with the
number of wait states for a MOVX instruction. This value can
range from 0H to 7H. "
But really when I tried to write a number to the SFR with address 09FH, the programs stops working.
By the way, this SFR is absent in the SFRs table.
Is this register really exist?