Counters.md

tags	cm12002 CS
links	[[Computer Systems Architectures]]
presentations	W19_L01_P01

Counters

• A counter is a [[./Registers.md | register]] that can be incremented by 1.
• After the maximum is achieved, next increment sets counter to 0.
• Register of n [[./Sequential Logic.md | flip-flops]] can count up to $2^n - 1$. For example, with 4 bits (i.e. 4 flip-flops) the counter starts at 0 and resets after reaching $2^4 - 1 = 15$.
• One example of a counter is the PC (Program Counter).
• There are two types of counters:

  1. Asynchronous (also known as the ripple counter) — the change that occurs to increment the counter starts at one end and “ripples” through to the other end. For example, a 4-bit up counter that uses edge-triggered^[Edge-triggered means that the state changes with the falling edge of the clock pulse.] [[./Sequential Logic.md#Types of Flip-Flops| J-K flip-flops]]:^[There is no explanation of how it works in the book, however Fabio linked a video, which may or may not help.]

     ![[Attachments/Pasted image 20240211180030.png]]

     • However, the problem with ripple counters is that the delay is proportional to the length of the counter.

  2. Synchronous counters change all flip-flops of the counter at the same time. For example, a 3-bit synchronous counter using three [[./Sequential Logic.md#Types of Flip-Flops| J-K flip-flops]]:

     ![[Attachments/Pasted image 20240211180832.png]] ![[Attachments/Pasted image 20240211181322.png]] ![[Attachments/Pasted image 20240211181247.png]] ![[Attachments/Pasted image 20240211181357.png]]