Standard boxes control binary tags such as outputs or bit memories. An assignment box sets the binary tag if signal state “1” is present at the function input, and resets it again with signal state “0”. The reverse is true with the negated assignment box (Fig. 8.15).
Standard boxes exist for setting and resetting a binary tag or for pulse generation during evaluation of signal edges. Standard boxes can also be used to set and reset bit fields, to execute jumps in the program, and to terminate a block.
Standard boxes can be used within a logic operation, following a T branch, or as the termination of an operation. They can be positioned in series or parallel. A standard Fig. 8.14 Comparison functions in a binary logic operation
box standing on its own without a previous logic operation has the signal state “1”
at the function input.
8.3.1 Assignment and negated assignment
The result of the logic operation is directly assigned to the tag named above the as- signment box: with a logic operation result “1”, the tag is set, and with a logic oper- ation result “0”, it is reset. You can control several assignment boxes simultaneous- ly using the result of the logic operation by arranging the boxes in parallel (Fig. 8.16). All tags named above the coils react in the same manner (first logic op- eration).
With the negated assignment, the tag named above the box is set if the result of the logic operation is “0”; it is reset if the result of the logic operation is “1” (second logic operation): if the AND function with “Input 3” and “Input 4” is fulfilled, “Out- put 3” is set to signal state “0”.
Fig. 8.15 Overview of standard boxes Start timer
function
Reset timer function
Set time duration
Timer function Timer function Timer function
Standard boxes
FKT Time
RT PT
VALUE
PT FKT:
TP Accumulate time TON OFF delay TOF ON delay TONR Pulse time
Negated assignment Reset box
Binary tag Binary tag Binary tag Binary tag
Assignment Set box
= /= S R
Pulse on positive edge
Pulse on negative edge
Binary tag Binary tag
Edge trigger flag Edge trigger flag
P= N=
Multiple setting
Multiple resetting
Binary tag Binary tag
SET_BF RESET_BF
EN EN
NN
Jump with “1” Jump with “0”
Jump destination Jump destination
JMP JMPN
Conditional block end Binary tag
RET
The third logic operation shows the position of an assignment within an operation.
The tag “Output 4 “ is set if “Input 5” and “Input 6” both have signal state “1”.
If “Input 7” also has signal state “1”, the tag “Output 5” is set.
You can position further binary logic operations following a T branch or in front of the assignment (bottom operation). The result of the logic operation is not influ- enced by an assignment box positioned within an operation. Assignment boxes po- sitioned in series react like parallel ones.
8.3.2 Set and reset boxes
With the logic operation result “1” on the set box, the binary tag named above the box is set to the signal state “1”. With the logic operation result “1” on the reset box, the tag named above the box is reset to the signal state “0”. With the logic operation result “0” on the set or reset box, the binary tag remains uninfluenced (Fig. 8.17).
You can position several set and reset boxes in any combination in the same logic operation and also together with assignment boxes.
As with the assignment box, you can position the set and reset boxes within a logic operation or following a T branch. Without a previous logic operation (with func- tion input open), the box is always activated.
Fig. 8.16 Assignment and negated assignment
8.3.3 Edge evaluation with pulse output in the function block diagram The P= and N= boxes are available for edge evaluation with pulse output. The binary tag named above the P= box is set for the duration of one program cycle if the logic operation result of the previous operation changes from signal state “0” to “1” (ris- ing edge).
With the N= box, the binary tag named above the box is set for the duration of one program cycle with a falling edge of the previous operation (change in logic opera- tion result from “1” to “0”) (Fig. 8.18).
The binary tag named above the box is referred to as a “Pulse bit memory”. Suitable for pulse bit memories are operand types which are not connected “outside” to modules, for example tags from the bit memory or data areas. The edge trigger flag is named under the box, and must be a different tag for each edge evaluation (see Chapter 10.3 “Edge evaluation” on page 338).
The edge boxes can be positioned within a logic operation or terminate an opera- tion. Edge boxes can also be programmed following a T branch.
Fig. 8.17 Set and reset boxes
Fig. 8.18 Edge evaluation of logic operation result (with “pulse bit memory”)
8.3.4 Multiple setting and resetting (filling of bit field) in the function block diagram
With the logic operation result “1” at the EN input, the SET_BF box sets a bit field to signal state “1”. The bit field is defined by the start tag named above the box and the number of bits at the function input N. With the logic operation result “1”, the RESET_BF box resets the bits in the bit field.
There is no response if the result of the logic operation at the EN input is “0”. If the SET_BF and RESET_BF boxes do not have a previous operation, they are always exe- cuted.
In the example in Fig. 8.19, the bit field for the SET_BF box is defined by the start tag “Bitfield0” which is followed by seven bits (thus a total of eight bits). The bit field for the RESET_BF box is in the data block “Data80”, commences with the field (binary) component Bitfield[1], and ends after 15 subsequent bits.
8.3.5 Starting IEC timer functions in the function block diagram with standard boxes
You can use the timer functions to implement timing processes in the program such as waiting and monitoring times, measurement of a time interval, or the generation of pulses. An IEC timer function can be started with two different program elements: with a standard box or with a Q box (see Chapter 8.4.5 “Control- ling IEC timer functions in the function block diagram with Q boxes” on page 267).
Both variants are equally useful. A detailed description of the timer functions is provided in Chapter 10.4 “Time functions” on page 344.
A timer function can be started with one of the four behavior patterns TP, TON, TOF, and TONR. A timer function requires internal data for each application. You can specify where this data is to be saved when programming: For the Single instance entry in its own data block with the data type IEC_TIMER and for the Multi-instance Fig. 8.19 Filling of bit field with SET_BF and RESET_BF
entry in the instance data block of the calling function block with a data type that depends on the behavior of the timer function (TP_TIME, TON_TIME, TOF_TIME, TONR_TIME). You address a timer function with the name of the instance data – data block or local data.
The standard box for starting a timer function requires a preceding logic operation.
It can only be placed at the end of a logic operation. Under the standard box is the duration with which the timer function is started.
A timer function is reset using the RT box. The RT box can be programmed in the middle of a logic operation or as its termination.
The PT box sets the duration of a timer function. Each processing with signal state
“1” overwrites the duration in the instance data with the value given under the box.
Fig. 8.20 shows the standard boxes used in connection with IEC timer functions. In the first logic operation, the timer function in the local data with the name #Timer_- function is started as ON delay with the value #Duration. The status of the timer function can be scanned with the structure component Q. The example shows start- ing the timer function, resetting the timer function, and setting the duration with a rising edge.
Fig. 8.20 Processing a timer function with standard boxes