Test portion of two values to see whether they are equal. Compares 16 bit data of a source address to 16 bit data at a reference address through a mask.
Example
Lets say we have four counters. Each counter goes from 0 to 9. Since 0 to 9 can be represented in 4 bits then we can combine the four counters in one word of 16 bits. This is to reduce the amount of memory counters will need.
- Counter 1 = N7:0 bit 0,1,2,3
- Counter 2 = N7:0 bit 4,5,6,7
- Counter 3 = N7:0 bit 8,19,10,11
- Counter 4 = N7:0 bit 12,13,14,15
Now that we have all four counters in one word we want to compare our result to a certain value. MEQ is the solution for such a problem. MEQ will make a comparison of a value based on the bits specified in the mask section.
Ladder Logic Solution
Comparing N7:0 = -31166 with 2 is energizing B3:0/0 why? Well cause:
- Source: -31166 = 8642 Hex
- Compare: 0002 = 0002 hex
Comparing N7:0 = -31166 with 64 is energizing B3:0/1 why? Well cause:
- Source: -31166 = 8642 Hex
- Compare: 0064 = 0040 Hex
Comparing N7:0 = -31166 with 1536 is energizing B3:0/2 why? Well cause:
- Source: -31166 = 8642 Hex
- Compare: 0600 = 0002 Hex
Comparing N7:0 = -31166 with -32768 is energizing B3:0/3 why? Well cause:
- Source: -31166 = 8642 Hex
- Compare: 0002 = 8000 Hex
Note
- When the mask is equal to F = 1111 in Binary. So if you want to mask only the first 3 bits out of 4 then your mask should be 0111, which is equal to 7 in Hex. What this mean is that your binary bit is on then the comparison would be done on that specific bit or bits.
