RAM16K Chip

1. RAM16K Chip

RAM16K is a memory chip consisting of 16,384 (2¹⁴) 16-bit words. It is constructed from 4 RAM4K chips. The chip takes a 14-bit address (address[14]) to select one of its 16K memory locations.

The top 2 address bits (address[12..13]) select which of the 4 RAM4K chips to use.

The bottom 12 bits (address[0..11]) select the register within the chosen RAM4K.

2. Truth Table

address (14-bit)	in (16-bit)	load	out (16-bit)	Notes
00000000000000	0000000000000000	0	previous value	Reads old value from address 0
00000000000001	0000000000001111	1	0000000000001111	Writes to address 1
00000000000001	0000000000000000	0	0000000000001111	Reads value back from address 1
11111111111111	1010101010101010	1	1010101010101010	Writes to last address (16383)
11111111111111	0000000000000000	0	1010101010101010	Reads value from last address

3. Implementation (HDL)

RAM16K is built using 4 RAM4K chips. The upper 2 address bits (address[12..13]) select the chip, and the lower 12 bits (address[0..11]) index into it.

CHIP RAM16K {
    IN in[16], load, address[14];
    OUT out[16];

    PARTS:
    DMux4Way(in=load, sel=address[12..13], a=la, b=lb, c=lc, d=ld);

    RAM4K(in=in, load=la, address=address[0..11], out=ra);
    RAM4K(in=in, load=lb, address=address[0..11], out=rb);
    RAM4K(in=in, load=lc, address=address[0..11], out=rc);
    RAM4K(in=in, load=ld, address=address[0..11], out=rd);

    Mux4Way16(a=ra, b=rb, c=rc, d=rd, sel=address[12..13], out=out);
}