FP_BCC

Block check character calculation

This FP instruction calculates the block check character (BCC) according to the calculation specified by s1_Control. The data is specified by the start address s2_Start and the number of bytes n_Bytes. The BCC is stored in the 16-bit area specified by d.

Parameters

Input

s1_Control (WORD, INT, UINT): Calculation method
s2_Start (WORD, INT, UINT): Starting address
n_Bytes (WORD, INT, UINT): Number of bytes

Output

d (WORD, INT, UINT): Block check character

Remarks

Specifying the control code s1_Control

(1) Calculation method
0: Addition (SYS_BCC_CALCULATION_METHOD_ADD)

1: Subtraction (SYS_BCC_CALCULATION_METHOD_SUB)

2: Exclusive OR (SYS_BCC_CALCULATION_METHOD_XOR)

16#A: CRC-16 (SYS_BCC_CALCULATION_METHOD_CRC16)
(2) Calculation starting position (bytes from s2_Start)
16#0–16#F
(3) Storage starting position (bytes from d)
0: Binary data (1 byte)

1: ASCII data (2 bytes)
(4) Data to be converted

Error flags

sys_bIsOperationErrorHold (turns to TRUE and remains TRUE): if the area specified using the index modifier exceeds the limit.
sys_bIsOperationErrorNonHold (turns to TRUE for one scan): if the area specified using the index modifier exceeds the limit.

Example

POU header

All input and output variables used for programming this function have been declared in the POU header.The same POU header is used for all programming languages.

	VAR
		bStart: BOOL:=FALSE;
			(*activates the function*)
		iBCC_Calc_Method: INT:=2;
		sASCII_String: STRING[32]:='%01#RCSX0000';
			(*specifies the operation:
0: addition
1: subtraction
2:XOR*)
		wBCC: WORD:=0;
			(*result after a 0->1 leading
edge from start: 10#172*)
	END_VAR

POU body

When bStart turns to TRUE, a block check character calculation is performed on sASCII_String. The calculation method is exclusive OR. (Use this method when large amounts of data are transmitted).

Exclusive OR operation:

bvar_1	bvar_2	bvar_3
0	0	0
0	1	1
1	0	1
1	1	0

The binary codes of the first two characters are compared with each other to yield an 8-character exclusive OR operation result. This result is then compared to the binary code of the next character, and so on until the final character is reached. The last exclusive OR result is the block check character.

BCC calculation using exclusive OR operation:

(1) ASCII-HEX-code
(2) ASCII-BIN-code
(3) Exclusive ORing
(4) calculation
(5) Block Check Character (BCC)
(6) Calculation result (16#1D) is stored in d.

LD body

BODY
    WORKSPACE
        NETWORK_LIST_TYPE := NWTYPELD ;
        ACTIVE_NETWORK := 0 ;
    END_WORKSPACE
    NET_WORK
        NETWORK_TYPE := NWTYPELD ;
        NETWORK_LABEL :=  ;
        NETWORK_TITLE :=  ;
        NETWORK_HEIGHT := 11 ;
        NETWORK_BODY
B(B_CONTACT,,bStart,3,2,5,4,);
B(B_VARIN,,iBCC_Calc_Method,24,3,26,5,);
B(B_F,Adr_Of_VarOffs_I!,,16,5,25,9,,?D@'Var'?DOffs?CAdr);
B(B_VAROUT,,wBCC,33,3,35,5,);
B(B_VARIN,,sASCII_String,11,4,13,6,);
B(B_VARIN,,2,14,7,16,9,);
B(B_F,LEN!,,16,8,21,11,,?DIN?C);
B(B_F,FP_BCC!,,26,1,33,7,,?DEN?Ds1_Control?Ds2_Start?Dn_Bytes?AENO?Cd);
L(16,5,16,7);
L(13,5,16,5);
L(13,5,13,10);
L(13,10,16,10);
L(25,5,25,7);
L(25,5,26,5);
L(26,6,26,10);
L(21,10,26,10);
L(5,3,26,3);
L(1,3,3,3);
L(1,0,1,11);
        END_NETWORK_BODY
    END_NET_WORK
END_BODY

In this example, Adr_Of_VarOffs_I is used to create an offset of 2 words to compensate for the string's start code. By using LEN, the BCC calculation is performed on the entire data string.

ST body

IF bStart then
    FP_BCC(s1_Control := iBCC_Calc_Method,
           s2_Start := Adr_Of_VarOffs( Var:= sASCII_String, Offs:= 2),
           n_Bytes := LEN( sASCII_String),
           d => wBCC);
END_IF;