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As normal expressions that are the most deeply nested between brackets will be solved first. (Note: when in doubt use brackets to ensure you get the sequence you expect.)

! () XPY, ** SQR, TOD, FRD, NOT, NEG, LN, LOG, DEG, RAD, SIN, COS, TAN, ASN, ACS, ATN *, /, MOD +, - AND (for word) XOR (for word) OR (for word) >, >=, =, <=, <, <> AND (bit) XOR (bit) OR (bit) ladder instructions

Figure 19.13 Operator Precedence

plc st -19.10

• Language structures include those below,
IF-THEN-ELSIF-ELSE-END_IF; normal if-then structure
CASE-value:-ELSE-END_CASE; a case switching function
FOR-TO-BY-DO-END_FOR; for-next loop
WHILE-DO-END_WHILE;

Figure 19.14 Flow Control Functions

• Special instructions include those shown below.

RETAIN() causes a bit to be retentive IIN(); immediate input update EXIT; will quit a FOR or WHILE loop EMPTY

Figure 19.15 Special Instructions

• Consider the program below to find the average of five values in floating point memory.

plc st -19.11

F8:10 := 0; FOR (N7:0 := 0 TO 4) DO F8:10 := F8:10 + F8:[N7:0]; END_FOR;

Figure 19.16 A Program To Average Five Values In Memory With A For-Loop

• Consider the program below to find the average of five values in floating point memory.

F8:10 := 0;

WHILE (N7:0 < 5) DO F8:10 := F8:10 + F8:[N7:0]; N7:0 := N7:0 + 1;

END_WHILE;

Figure 19.17 A Program To Average Five Values In Memory With A While-Loop

• The example below will set different outputs depending upon the stat of an input.

plc st -19.12

IF (I:000/00 = 1) THEN O:001/00 := 1;

ELSIF (I:000/01 = 1 AND T4:0/DN = 1) THEN O:001/00 := 1; IF (I:000/02 = 0) THEN O:001/01 := 1; END_IF;

ELSE O:001/01 := 1; END_IF;

Figure 19.18 Example With An If Statement

• The example below will set output bits 00-03 depending upon the value of the integer in N7:0, if the value is not between 0 and 3 the outputs will all go off.

CASE N7:0 OF

0: O:000/00 := 1;

1: O:000/01 := 1;

2: O:000/02 := 1;

3: O:000/03 := 1; ELSE

O:000 := 0; END_CASE;

Figure 19.19 Use of a Case Statement

• The example below accepts a BCD input from (I:000) and will use it to change

plc st -19.13

the delay time for an on delay timer that will examine input I:002/00 drive output O:001/

00.

FRD (I:000, DELAY_TIME); IF (I:002/00) THEN TON (T4:0, 1.0, DELAY_TIME, 0); ELSE