Question

Describe how to modify the circuit of Figure tal capacity of 16K x 8. Use the same type of PROM chips. so that it has a to- A13 3-line-to-8-line B. 74ALS138 3 A 1-of-84b trol bus K3 E3 decoder 5 KO E2 Ag-A1o Ag-Aso E1 PROM-3 CS 2K x 8 Decoder selects one PROM chip determined by As1 and A1z or-Oo 18) 18] (81 D, Data bus (8) O%

Answer 1

Add 4 new PROM'S in addition to the four PROM'S in figure and Connect the chip select lines of four new 2K*8 PROM'S with names PROM-4,PROM-5,PROM-6 and PROM-7 to the outputs 4,5,6 and 7 of the 74ALS138 decoder respectively,then we have a total of eight PROM'S of each 2KB,so the total capacity of our new memory chip is 8*2KB=16KB.The connections for PROM-4,5,6 and 7 is similar to the PROM-0,1,2 and 3 i.e data bus and address bus connections are same for all the eight PROM'S except Chip select line connections, which are connected to output lines of 74ALS138-Decoder.