Random Access Memory
It's time to gather our knowledge of digital memory and create the ultimate storage unit: Random Access Memory or RAM for short. You might heard of things like "my computer ran out of RAM" or "xxx app drained my RAM real quick". These illustrate how important RAM is to the function of our computer. The reason why we rely on RAM so much is because it's blazing fast and the location of the memory doesn't not influence access speed, hence the name "random access memory". An additional magic is that no matter how much stuff our RAM stores, the access time is constant. So a RAM with 10 gigabytes is just as fast as one with 10 megabyte even though the first one stores 1000 times more stuff than the second. Before we move on to explore RAM more, you should watch Computerphile's clear explainations of RAM first:
RAM2
After watching the two videos, let's start by creating RAM with 2 flip flops:
It's your turn to implement the above in Sim. Here's the header:
ram2 clk input[n] address[1] -> [n]If you get stuck, click on "See Hints".
Fill in the blanks below:
ram2 clk input[n] address[1] -> [n] =
let
clk_a =
___________________
clk_b =
___________________
out_a =
___________________
out_b =
___________________
out =
___________________
in
outIf you completed the ram2, you may start to realize that we already built parts of it before. The way we connect the address to the clk signals of the two flip flops is just a regular dmux. The way we connect the two qs of the two flip flops to the final output is just a regular mux. Now with the same header, try implement ram2 again using dmux and mux.
ram2 clk input[n] address[1] -> [n]If you get stuck, click on "See Hints".
Fill in the blanks below:
ram2 clk input[n] address[1] -> [n] =
let
{ a = clk_a, b = clk_b } =
___________________
out_a =
___________________
out_b =
___________________
out =
___________________
in
outRAM8
Now that you know how to address 2 flip flops in a RAM, we can easily expand it into 8 flip flops:
ram8 clk input[n] address[3] -> [n]If you get stuck, click on "See Hints".
Fill in the blanks below:
ram8 clk input[n] address[3] -> [n] =
let
{ a = clk_a, b = clk_b, c = clk_c, d = clk_d
, e = clk_e, f = clk_f, g = clk_g, h = clk_h
} =
___________________
out_a =
___________________
out_b =
___________________
out_c =
___________________
out_d =
___________________
out_e =
___________________
out_f =
___________________
out_g =
___________________
out_h =
___________________
out =
___________________
in
outRAM64
Combine 8 RAM8 to form RAM64.
ram64 clk input[n] address[6] -> [n]RAM512
Combine 8 RAM64 to form RAM512.
ram512 clk input[n] address[9] -> [n]RAM4K
Combine 8 RAM512 to form RAM4K.
ram4k clk input[n] address[12] -> [n]RAM16K
Combine 4 RAM4K to form RAM16K. Not 8 this time, but 4.
ram16k clk input[n] address[14] -> [n]🎉 Congrats! You have created the memory unit of our computer!
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