COMPARE Mode, Result

Function
Enable or disable the SX comparator, compare voltages on RB.1 and RB.2, and retrieve comparison result to store in Result.

• Mode is a variable or constant (0 – 2) that enables or disables the comparator (RB.1 and RB.2) and determines if the optional comparator output pin (RB.0) is enabled or not. See the table below for an explanation of the Mode values.
• Result is a variable (usually a bit) in which the comparison result is stored.

Quick Facts

	SX18 / SX20 / SX28 / SX48 / SX52
Mode values	0: Disables comparator.
	1: Enables comparator with RB.0 as Result output.
	2: Enables comparator without RB.0 as Result output.
Result values	0: Voltage RB.1 > RB.2; RB.0 optionally outputs 0.
	1: voltage RB.1 < RB.2; RB.0 optionally outputs 1.

Explanation
The COMPARE instruction enables or disables the built-in comparator hardware on the SX's pins RB.0, RB.1, and RB.2. I/O pins RB.1 and RB.2 are the comparator inputs and RB.0 is optionally the comparator result output pin.

By default, the comparator feature is disabled. Using the COMPARE instruction with a Mode argument of 1 or 2 enables the comparator feature (using input pins RB.1 and RB.2) and returns the result of the comparison in Result. If Mode is 1, the result of the comparison is also output on I/O pin RB.0. The following is an example of the COMPARE instruction:

  COMPARE 1, result                             ' enable comparator, output result on RB.0

This example enables the comparator (setting RB.0 to output the result, with RB.1 and RB.2 as the comparator inputs) and writes the result of the comparison into result. Both result and the output pin RB.0 will be 0 if the input voltage on RB.1 was greater than that of RB.2. Result and the output pin RB.0 will be 1 if the input voltage on RB.1 was less than that of RB.2.

The following are points to remember with Comparator mode:

• Port B I/O pins 1 and 2 are the comparator inputs and I/O pin 0 is, optionally, the comparator result output.
• Port B I/O pin 0 may be used as a normal I/O pin by setting the OE bit of the Comparator register (COMPARE modes 0 and 2).
• The comparator is independent of the clock source and thus will operate even if the SX chip is halted or in SLEEP mode. To avoid spurious current draw during SLEEP mode, disable the comparator.

Related project: 8-bit ADC