This is a simple approach with intentional bugs in the solution to lab manual exercise in downloadable PLC Training Certificate course at https://bin95.com/allen-bradley-plc-programming.htm Simple solution for tracking Day of week (Mon,tues, etc.) part of HVAC scenario 3 (page 109 of Lab Manual). Last rung comment also give 2 alternate solutions (newer plc solution, and complex formula solution.) After you write into a PLC and debug, test (or you are having diffulty making it work on your PLC, see https://www.slideshare.net/bin95/plc-programming-example-day-of-week-answ for one possble working solution.

1. Https://BIN95.com
Simple Track Day of Week (M,T,W,T,F,S,S) © BIN95.com
On day of loading, pre plug C5.30.acc with value equal to what the current day of week is. (this is program setup) It simple and only requires minimum maintenance. The counter resets its
self when counter done bit fires. thus a virtual engine.
So for example, it is wednesday when you load the program, set C5:30.acc to = 3. If it was a friday, you would C5:30.acc to = 5. (Some PLC/PAC may need counter preset set at 8 instead
of 7.)
0000
EQU
Equal
Source A S:40
0<
Source B 23
23<
EQU
Clock
Calendar
Hours
EQU
Equal
Source A S:41
0<
Source B 59
59<
EQU
Clock
Calendar
Minutes
CU
DN
CTU
Count Up
Counter C5:30
Preset 7<
Accum 0<
CTU
Day of week Counter
(1=Mon,2=Tue,3=Wed,
4=Thu,5=Fri,6=Sat,
7=Sun)
DOWCNT
C5:30
DN
Day of week Counter
(1=Mon,2=Tue,3=Wed,
4=Thu,5=Fri,6=Sat,
7=Sun)
DOWCNT/DN
RES
C5:30
Day of week Counter
(1=Mon,2=Tue,3=Wed,
4=Thu,5=Fri,6=Sat,
7=Sun)
DOWCNT
From there on out, C5:30.acc will keep track of what day of the week it is.
0001
LIM
Limit Test
Low Lim 6
6<
Test C5:30.ACC
0<
High Lim 7
7<
LIM
Day of week Counter
(1=Mon,2=Tue,3=Wed,
4=Thu,5=Fri,6=Sat,
7=Sun)
DOWCNT.ACC
B3:20
7
ON is Day of week
equals SAT or SUN.
(One time setup of
C5:30.acc with day
downloading. IE:3=w)
With a huge Gregorian claendar mathimatical formula, you can do it another way that it also acocunts for leap years and does not require setup value be entered. 10 differant programmers,
you could have 10 differnt ways to takle this one. Always opt for the simplist way when possible.
Formula: N = d + 2m + [3(m+1)/5] + y + [y/4] - [y/100] + [y/400] + 2 ("d"=S:39, "m"=S:38, "y"=S:37, "N"=day of week 0-6)
(On some PLC processor, you have a Status word you can use that already has value 0-6 for date. Like SLC 500/3-5 uses S:53, where 0=Sunday, 6=Saturday)
0002
B3:20
7
ON is Day of week
equals SAT or SUN.
(One time setup of
C5:30.acc with day
downloading. IE:3=w)
B3:40
0
Do something, except
sat and sun.
0003 END