Traffic light PLC project--simply question

[kindalost]

I am building the ladder logic for a 4 way traffic light intersection.
Please look at the code below and tell me what the "M0 through M8" means. I know T is timer but do not know the rest.

here:


Name Input/Output

INPUT PLC :
X000 ; Switch ON/OFF Traffic Light.

OUTPUT PLC :
Y000 ; Red Color Lights in Position A.
Y001 ; Green color lights in Position A.
Y002 ; Red Color Lights in Position B.
Y003 ; Green color lights in Position B.
Y004 ; Red Color Lights in Position C.
Y005 ; Green color lights in Position C.
Y006 ; Red Color Lights in Position D.
Y007 ; Green color lights in Position D.


Step 1 :
Sequence for Green Light
a.If X000= ON Then System Traffic Light is Active.
Green Light in Position A = ON
b.If X000= ON And ( M0 = ON or T3 = ON ) And M2 = OFF Then M1 = ON ( Hold ON ) And T0 Activated.
Green Light in Position C = ON
c.If X000= ON And T0= ON And M3 = OFF Then M2 = ON ( Hold ON ) And T1 Activated.
Green Light in Position D = ON
d.If X000= ON And T1= ON And M4= OFF Then M3= ON ( Hold ON ) And T2 Activated.
Green Light in Position B = ON
e.If X000= ON And T2= ON And M1= OFF Then M4= ON ( Hold ON ) And T3 Activated.
f.If T3= ON And Goto Step 1.a.

Set timer= 2min

Step 2 :
Sequence for Red Light
a.If X000= ON And ( M2 = ON Or M3 = ON Or M4 = ON ) Then M5 = ON.
b.If X000= ON And ( M1 = ON Or M2 = ON Or M3 = ON ) Then M6 = ON.
c.If X000= ON And ( M1 = ON Or M3 = ON Or M4 = ON ) Then M7 = ON.
d.If X000= ON And ( M1 = ON Or M2 = ON Or M4 = ON ) Then M8 = ON.

Step 3 : Output PLC
a.If X000= ON And M5 = ON Then Y000 = ON.
b.If X000= ON And M1 = ON Then Y001 = ON.
c.If X000= ON And M6 = ON Then Y002 = ON.
d.If X000= ON And M4 = ON Then Y003 = ON.
e.If X000= ON And M7 = ON Then Y004 = ON.
f.If X000= ON And M2 = ON Then Y005 = ON.
g.If X000= ON And M8 = ON Then Y006 = ON.
h.If X000= ON And M3 = ON Then Y007 = ON.

 

[kindalost]

anyone????