**new**
i think i may not be clear ? i am saying pin 1 and pin 27 of the memory chip are connected on the controller board so that would cause special consideration if one wanted to use a 27c512 ?
ROM
the
as
close , it is a series of sections of 64 duplicate bytes followed by another section of 64 duplicate bytes..... all the waty to the end
each section of byte values is different and i get the exact same series for each successive chip reading attempts.
unless i choose a different chip size like 27c128 then the series of byte duplicates changes. where the first set maybe 7A in place of the 02
here is a clip from begining of my read
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till the end
I mapped the pins on the board so as to be reasonably certain that the ROM chip was compatible with the 27cXXX series of chips
all the pin/address/data lines seem to be consistent with the
27cXXX series pin out. the data and address lines match to the MCU adressing pins according to 27cXXX datasheet even the funny 8 through 11 pin jumble.(pin 22) ROM goes to (pin 29) 8051 (PSEN- prog store enable) (pin 20) ROM goes to (pin 30)8051 (ALE-Addr Latch Enable)
on the PCB the 8 data lines are all connected with the first 8 Address lines so D0 is connected to A0 and (D1 to A1) and these shared connection s all go back to MCU
thanks for the help, robb