MSP430G2211: Pin Assignments for Comparator Modules

Hello Vijayraj,

sorry for the misleading code example, which is including even a mistake.

So please let me bring some light into the Comparator input selection.

First let's take at the selection of the Comparator function for P1.1 in the given code example. Let's analyze the multiplexer selection. The P1.1 is equipped with the CA1 function. This is specified in the datasheet table 16.

The next step is looking into the User's Guide and the input multiplexers in Figure 21-1

Here you can see, that in case the swap multiplexer control bit CAEX=0 the input for the positive Comparator input is defined by the upper input multiplexer. Looking at the multiplexer options, again you can see to select CA1, you need to set P2CA4 to 1 and P2CA0 to 0.

That's what is done with the instruction CACTL2 = P2CA4;

Looking at your question, how to select P1.5 for CACTL2, it's a bit misleading. One has to ask "what pin do you intend to connect to which Comparator input?".

Let's assume, you want to connect P1.5 to the positive Comparator input. Looking into the datasheet you can see in table 17

that at P1.5/CA5 is available. Looking again into the block diagram of the User's Guide, you can see the upper multiplexer does not support the connection to CA5. So the only possibility selecting CA5 is using the lower multiplexer. To connect the lower multiplexer to the positive input of the Comparator, you need to set CAEX =1, and to select CA5 the control bits of the multiplexer need to be 101, means P2CA3 = 1, P2CA2 = 0 and P2CA1 = 1.

To maintain the same functionality as in the given code example now you have to apply the threshold voltage to the negative input, and thus due to CAEX = 1 now CARSEL needs to be = 0. So CACTL1 = CAREF0 + CAON;

I hope this explanations helps you to understand the complex settings.

The mistake of the code example I mentioned above, is the missing setting of CAPD for P1.1. This is required to disable the input buffer, to avoid a floating node and respective currents, when applying analog voltage levels to P1.1.

In your case, you'd need to set it for P1.5.

Best regards

Peter