E9.7 A 32KB EPROM needs a starting address of 30000, and a 32KB RAM needs a star

Question

E9.7 A 32KB EPROM needs a starting address of 30000, and a 32KB RAM needs a starting address of 20000. The circuitry in Figure 9.17 shows how these addresses are partially decoded. In this example, three-input NAND gates are used to do the decoding. All three inputs must be high for the output to go low (and enable the memories). IOM is inverted, so that it presents a 1 when low. A17 is connected directly, because it is high in both the RAM and EPROM address ranges. Only Al6 changes. It is low for the RAM range and high for the EPROM range. Address lines Ao through A 4 are used by the memories themselves. FIGURE 9.17 Partial-address decoder for 32KB EPROM at 30000, and 32KB RAM at 20000 90 200 RAMSEL 16 ROMSEL Can you determine the range of addresses for each memory?

Explanation / Answer

Solution:

32 KB EPROM to be interfaced with 32 KB RAM
Starting address of EPROM 30000
Starting address of EPROM 20000

No.of.Address lines required: A0 to A17

A17 direct connection
A16 only changed

EPROM
   Base address    : 30000
   Size       : 32KB
   End address       = Based Address + (Size in Hex) - 1  
               = 30000 + 8000 – 1
               = 37FFF
RAM:
       Base address    : 20000
   Size           : 32KB
   End address       = Based Address + (Size in Hex) - 1  
               = 20000 + 8000 – 1
               = 37FFF

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