Mictrocontroller Week 03
With 10 pins or 10 bits, a PROM can address 210 which is 1024 memory locations = 1 kB
Four PROM chips will have 4 kB of addressable memory
Microprocessor (12 address bits) can access 212 = 4096 = 4 kB locations (0x1000)
Connect MP address lines A9-A0 to PROM's A9-A0 pins
But what do we do with MP's A11 and A10 address lines?
Connect by the below ==> each PROM chip will be selected upon the state (1 or
0) of MP's A11 and A10 lines
So addresses 00 00 0000 0000 - 00 11 1111 1111 (0x000-0x3FF)
01 00 0000 0000 - 01 11 1111 1111 (0x400-0x7FF)
10 00 0000 0000 - 10 11 1111 1111 (0x800-0xBFF)
11 00 0000 0000 - 11 11 1111 1111 (0xC00-0xFFF)
Three inputs NAND chip and scheme
Scheme used four of the PROM chips and four three-input NAND gates (CS =
chip select pins)
Scheme to coonect 12 input pins MP address to four PROM 10 address pins
== MEMR (Merory Read)
11
annaabi.ee 
