backendcode
Member
Hello guys,
I was reading programming manual of Allen Bradley and they mentioned few tips and I want to clear one tip
tip: I/O module data updates asynchronously to the execution of logic. If you reference an input multiple times in your logic, the input could change state between separate references. If you need the input to have the same state for each reference, buffer the input value and reference that buffer tag.
Let me make few things clear, and please correct me if I am wrong.
As I know/read somewhere, Compactlogix and control logix processors update data asynchronously which means Input and output card tell processor itself when the input and output value change and then processor update those values during execution of the program.
Where in PLC 5, an update is synchronous meant PLC first read the value of the input and then execute the program and if during execution the program, input value gets change, processor won't find it until it reads those input in next cycle.
Are they referring this in above tips? Please tell me what is buffer tag?
I assume, put the input value into an internal bit (Internal bit tag) and refer that internal bit everywhere wherever you want to use that input value?
Can you please help me to understand this concept?
Thanks,
I was reading programming manual of Allen Bradley and they mentioned few tips and I want to clear one tip
tip: I/O module data updates asynchronously to the execution of logic. If you reference an input multiple times in your logic, the input could change state between separate references. If you need the input to have the same state for each reference, buffer the input value and reference that buffer tag.
Let me make few things clear, and please correct me if I am wrong.
As I know/read somewhere, Compactlogix and control logix processors update data asynchronously which means Input and output card tell processor itself when the input and output value change and then processor update those values during execution of the program.
Where in PLC 5, an update is synchronous meant PLC first read the value of the input and then execute the program and if during execution the program, input value gets change, processor won't find it until it reads those input in next cycle.
Are they referring this in above tips? Please tell me what is buffer tag?
I assume, put the input value into an internal bit (Internal bit tag) and refer that internal bit everywhere wherever you want to use that input value?
Can you please help me to understand this concept?
Thanks,
