S7-1200 TIA Portal FIFO implementation

My implementation of circular FIFO based on example from help. It will work with any datatype.

This very basic code but i hope this gives you idea how its works

For more details look on screenshots in attached file

IF NOT #getBufSize THEN
#buffer_size := CountOfElements(#Buffer);
#getBufSize := TRUE;
END_IF;


IF #FlushBuf THEN
#tail := 0;
#head := 0;
#count := 0;
#FlushBuf := FALSE;
END_IF;

IF #Enqueue THEN
IF #count < #buffer_size THEN
#internalError :=
MOVE_BLK_VARIANT(SRC := #Enqueue_Data,
COUNT := 1,
SRC_INDEX := 0,
DEST_INDEX := #tail,
DEST => #Buffer);
#count := #count + 1;
#tail := #tail + 1;
IF #tail = #buffer_size THEN
#tail := 0;
END_IF;
END_IF;
END_IF;

IF #Dequeue THEN
IF #count > 0 THEN
#internalError := MOVE_BLK_VARIANT(SRC := #Buffer,
COUNT := 1,
SRC_INDEX := #head,
DEST_INDEX := 0,
DEST => #Dequeue_Data);
#count := #count - 1;
#head := #head + 1;
IF #head = #buffer_size THEN
#head := 0;
END_IF;
END_IF;
END_IF;

In the Library of General Funtions LGF you will find a FIFO. It's an open block if you want to see how it could be done.

You will find the Libtrary here: https://support.industry.siemens.com/cs/us/en/view/109479728

BR Sven

Hi

You can use method from mine moving average calculation:

1. data block  - array with length as Your FIFO

2. on new data:

a. Buffer[Pointer]-->Output;

b. Buffer[Pointer]:=New_Data;

c. Pointer++;

d. if (Pointer>=FIFO_Len)  Pointer:=0;

e. Sum:=Sum+New_Data-Output;

f. Average:=Sum/FIFO_Len;

in this example Buffer is Array[0..FIFO_LEN-1]

the e. and f. are required if you want to use FIFO for calculating average over FIFO_Len entries.

if you have it as Integer and are using CALCULATE function choose DINT under Calculate

to prevent arithmetic overflow.

UPDATE: New method of implementing circular buffer using modulo operator

CONST
BuffLen:=15; //must be 2^N-1 in order to work
END_CONST

VAR
FIFO[0..BuffLen] OF DINT;
RD_Pointer:DINT;
WR_Pointer:DINT;
END_VAR


IF WriteCmd THEN //write cmd
FIFO[WR_Pointer]:=Something;
WR_Pointer:=DWORD_TO_DINT(DINT_TO_DWORD(WR_Pointer+1) AND BuffLen);//increment write pointer
IF (WR_Pointer=RD_Pointer) THEN
BuffOverrun:=true;
END_IF;
END_IF;

IF ReadCmd AND (WR_Pointer<>RD_Pointer) THEN // read cmd
Something:= FIFO[RD_Pointer];
RD_Pointer:=DWORD_TO_DINT(DINT_TO_DWORD(RD_Pointer+1) AND BuffLen);
END_IF;

BuffSize:=DWORD_TO_DINT(DINT_TO_DWORD(WR_Pointer-RD_Pointer) AND BuffLen);

 It can be rewritten in the form of arbitrary buffer lenghth using modulo operation, to get rid of AND masking the buffer length of 2^N.

CONST
BuffLen:=20;
END_CONST

VAR
FIFO[0..BuffLen-1] OF DINT;
RD_Pointer:DINT;
WR_Pointer:DINT;
END_VAR


IF WriteCmd THEN //write cmd
FIFO[WR_Pointer]:=SomethingInput;
WR_Pointer:=(WR_Pointer+1) % BuffLen);//increment write pointer
IF (WR_Pointer=RD_Pointer) THEN
BuffOverrun:=true;
END_IF;
END_IF;

IF ReadCmd AND (WR_Pointer<>RD_Pointer) THEN // read cmd
SomethingOutput:= FIFO[RD_Pointer];
RD_Pointer:=(RD_Pointer+1) % BuffLen);
END_IF;

BuffSize:=(WR_Pointer-RD_Pointer + BuffLen) % BuffLen); //using modulo to calculate fill size

I am attaching my implementation of a circular queue (or FIFO). Is very simple and if you want different size buffer just change the array size of the queue datatype and update the MaxSize tag. 

Ask if you have any question using this queue.

Attachment extension: .zap14

New question published by Muralimohan is split to a separate thread with the subject Programm for tanks that had to be shifted.

Best regards
Jen_Moderator