# Difference between Shadow register, match register and capture compare register in a timer module

On page 704 of the data sheet of the Texas instrument Tiva C TM4C123GH6PM....it has these three registers in its timer module.i searched about these registers and found that shadow register is a register that holds the copy of a register , match register holds a value and compares the value with timer value and ccp register also do the same it captures and compares the value with the timer. if what i understood is right then i don't find any difference among these register but they are present. What is the difference between these registers?

• its a 32 bit micro-controller – hunter Oct 9 '20 at 0:08
• @jsotola could you tell me whats the difference – hunter Oct 9 '20 at 0:10
• @hunter, I'll look it up ... which microcontroller are you talking about? .... if you want to know what the difference is, then you should be asking that ... your post asks is there a difference? ... that is a yes/no question that can be answered without any research .... please edit your post so that it asks what you actually want to know – jsotola Oct 9 '20 at 0:25
• @jsotola i edited the question thanks for noticing. The micro-controller is arm cortex m4 and the embedded board is Texas instrument Tiva C TM4C123GH6PM. timer section is at page 704 of datasheet – hunter Oct 9 '20 at 1:23
• Would be better if you had said so from the start and linked the data sheet. Attempted to do that for you. Often the best way to figure things like this out is to look at example code for things like PWM out, and event capture in. Ultimately given how versatile some of these things are, it may be better to focus on a practical need and figure out what could achieve that, rather than trying to "learn the chip" in its entirety. – Chris Stratton Oct 9 '20 at 1:31

Each timer module contains a free running timer.

The value of that timer can be read at any time by reading the value of the Shadow register.

Since the timer continuously runs, you have to monitor its value if you want to use it to generate a periodic event.

This could be done in software by continuously reading the value of the Shadow register, or in hardware by setting a value in the Capture/Compare register. Think of an alarm clock as a real world example.

The Capture/Compare register circuitry is also connected to hardware pins that allow the timing of external events, and also to allow the generation of external events in the form of PWM output.

The Match register is used to set the desired intervals such as the PWM interval.

Look at section 1.3.4.4 on page 61.