Structure Text Programming

important think that we understand the structure text programming. sometime we use the structure text programming in allen bradley panelview plus to manipulate the instruction and to reduce the plc memory.If you know how to program in any high level language, such as Basic or C, you will be comfortable with Structured Text (ST) programming. ST programming is part of the IEC 61131 standard. An example program is shown in Figure below.

Structure Text Programming

 The program is called main and is defined between the statements PROGRAM an END_PROGRAM. Every program begins with statements the define the variables. In this case the ariable i is defined to be an integer. The program follows the variable declarations. This program counts from 0 to 10 with a loop. When the example program starts the value of integer memory i will be set to zero. The REPEAT and END_REPEAT statements define the loop. The UNTIL statement defines when the loop must end. A line is present to increment the value of i for each loop.One important difference between ST and traditional programming languages is the nature of program flow control. A ST program will be run from beginning to end many times each second. A traditional program should not reach the end until it is completely finished. In the previous example the loop could lead to a program that (with some modification) might go into an infinite loop. If this were to happen during a control application the controller would stop responding, the process might become dangerous, and the controller watchdog timer would force a fault.ST has been designed to work with the other PLC programming languages. For example, a ladder logic program can call a structured text subroutine.you can download the modulle about Structure Text Programming from here and i do hope it can useful for you.

Understanding Array Concept

Array:  a numerically indexed sequence of elements of the dame data type. An array tag occupies a continguous section of memory in the controller with each element in sequence. Array can have one, two or three dimensions.

Element : a single position within an array.

The elements in the array occupy memory in order. The array always start at 0 and extend to the numberof elements minus 1

an array in the tag windows is shown in the following graphic

An array must be created with the following rules in the mind:

• An array can have up to three dimensions unless it is a part of a structure, where then it can have only  one dimensions.
• An array can be of one data type only. Array support the following data type:

USB-to-Data Highway Plus Cable (USB2DHPLUS)

About the Cable
The 1784-U2DHP USB-to-Data Highway Plus Cable allows a customer to connect a computer to a Data Highway Plus (DH+) network via an unused USB port on the computer. You can also use the cable to connect the computer to PLC-5 processors (except for Classic PLC-5 processors, such as PLC-5/10, PLC-5/12, PLC-5/15, and PLC-5/25) or SLC 5/04 processors.

• Insert the end of the cable having the USB connector into an unused USB port on a computer.
  You see the Found New Hardware wizard.  

• if you do not see the Found New Hardware wizard, go on to step 9
  on page 7. Otherwise, continue with the next step.
• Select the No, not this time option and click Next.
• Select the Install from a list or specific location option and click Next.
• Select the Search for the best driver option.
• Check only the Include this location checkbox.
• Browse to the location where you saved the 1784_u2dhp.inf file and click OK or from program file >RockwellSoftware>RSLinx.

 

• Click Next.
• Follow the procedure
• Click Finish.

there is 2 ways to Configure the cable driver for use with your DH+ networked device

• DF1 serial 1770-KF2/1785-KE driver for RSLinx Classic Software, Version 2.52 and Earlier.
• Direct using USB2DHPLUS driver listed on RSLinx configure driver for RSLinx Classic Software, Version 2.53 and Later

for detail information abaut how to install USB2DHPLUS cable you can download from here