I am a begginer in the field of microcomputers and their architecture and recently I got an assignment with the following instructions:
With the use of the mapping table find out which adresses in IC2, IC3 and IC4 circuits occupy the system address space. In case of incomplete decoder list all address blocks in which the circuits are mirrored.
If I understood corectly, the system data bus has 8 bits - AD [0..7], and all of the mentioned ICs (IC2-4) has 8 bits on local data bus. If I'm correct, that means I can use 1:1 mapping. I made a table where I mapped the IC2 and IC3. On these two ICs the Chip Select pins are A15, so I could use logic 0 and 1 for selecting them.
|A15||A14||A13||A12||A11||A10||A9||A8||A7||A6||A5||A4||A3||A2||A1||A0||System Address Bus|
|A14||A13||A12||A11||A10||A9||A8||A7||A6||A5||A4||A3||A2||A1||A0||IC2 Local Address Bus|
|A14||A13||A12||A11||A10||A9||A8||A7||A6||A5||A4||A3||A2||A1||A0||IC3 Local Address Bus|
I am pretty sure that I missed something, because now I can not map the IC4. Also there are the WR#, RD# and PSEN# signals and 3 NAND gates below the 3 ICS, which have something to do with the IC4, but I do not know what.
Can someone please help to navigate me, what should I do?
Here is the scheme and the mentioned ICs are in the yellow-red square in the right part of the picture.