RSLogix Calculating 1st Monday of the Month

ksmohammed · May 7, 2018

Hey guys,

I need help calculating first Monday of the month. Has anyone ever had to perform such calculation? Rockwell has UFDB that calculates the Day of the Week.

thingstodo · May 7, 2018

ksmohammed said:
Hey guys,

I need help calculating first Monday of the month. Has anyone ever had to perform such calculation? Rockwell has UFDB that calculates the Day of the Week.

I suspect that I am mis-understanding the question, but here goes:

When you use the GSV to read the date and time into an array of dints, I call mine PLC_DateTime, index 0 is year, 1 is month, 2 is day

EQU PLC_DateTime[2] 1 ons First_Day_Oneshot ote Your_New_Tag

harryting · May 7, 2018

I would think you should be able to do that with a bit of code once you have the following:

- Day of the week
- Day of the month
- New month tracking bit

Once you enter a new month, you set the New Month tracking bit then look for Monday...

RonJohn · May 7, 2018

I don't think you'd even need the tracking bit, given that the first Monday (or any other day of the week) would occur no later than the 7th day of the month.

thingstodo · May 7, 2018

thingstodo said:
I suspect that I am mis-understanding the question, but here goes:

When you use the GSV to read the date and time into an array of dints, I call mine PLC_DateTime, index 0 is year, 1 is month, 2 is day

EQU PLC_DateTime[2] 1 ons First_Day_Oneshot ote Your_New_Tag

I *KNEW* that I had not understood the question ... why can't you see that sort of thing BEFORE you hit SUBMIT?

widelto · May 7, 2018

I would think of in only two conditions:
Day of week is monday ( this routine already exists) and day of the month (very easy to get) less than or equal to 6.
if those conditions are true the that is the first monday of the month.

JordanCClark · May 7, 2018

widelto said:
I would think of in only two conditions:
Day of week is monday ( this routine already exists) and day of the month (very easy to get) less than or equal to 6.
if those conditions are true the that is the first monday of the month.

Less than or equal to 7... Today is a good example.

widelto · May 7, 2018

Jordan, I wrote 7 and then changed my mind. Yes you are right.

JordanCClark · May 7, 2018

widelto said:
Jordan, I wrote 7 and then changed my mind. Yes you are right.

No worries, my friend. A good sanity check never hurts.

Unless it's from my wife. Then it can be painful. But you didn't hear that from me.

T Gibbs · May 7, 2018

I did that exact thing in Direct Soft 5 and Click for Daylight Savings time setting. It works perfectly.

chopin · May 8, 2018

I would do it this way

RSLogix Calculating 1st Monday of the Month

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