Function block - Manages a "last in / first out" stack
PUSH : BOOL Push a new value (on rising edge)
POP :
BOOL Pop a new
value (on rising edge)
RST : BOOL Reset the list
NEXTIN : ANY Value to be pushed
NEXTOUT : ANY Value at the top of the stack - updated after
call!
BUFFER :
ANY Array for storing
values
EMPTY : BOOL
TRUE if the stack is empty
OFLO : BOOL
TRUE if overflow on a PUSH
command
COUNT :
DINT Number of values in
the stack
PREAD :
DINT Index in the buffer
of the top of the stack
PWRITE : DINT Index in the buffer of the next push position
NEXTIN, NEXTOUT and BUFFER must have the same data type and cannot be STRING.
The NEXTOUT argument specifies a variable that is filled with the value at the top of the stack after the block is called.
Values are stored in the "BUFFER" array. Data is never shifted or reset. Only read and write pointers and pushed values are updated. The maximum size of the stack is the dimension of the array.
The first time the block is called, it remembers on which array it should work. If you call later the same instance with another BUFFER input, the call is considered as invalid and makes nothing. Outputs reports an empty stack in this case.
In LD language, input rung is the PUSH input. The output rung is the EMPTY output.
(* MyLIFO is a declared instance of LIFO
function block *)
MyLIFO (PUSH, POP, RST, NEXTIN, NEXTOUT, BUFFER);
EMPTY := MyLIFO.EMPTY;
OFLO := MyLIFO.OFLO;
COUNT := MyLIFO.COUNT;
PREAD := MyLIFO.PREAD;
PWRITE := MyLIFO.PWRITE;
(* MyLIFO is a declared instance of LIFO
function block *)
Op1: CAL MyLIFO (PUSH, POP, RST, NEXTIN, NEXTOUT, BUFFER)
LD MyLIFO.EMPTY
ST EMPTY
LD MyLIFO.OFLO
ST OFLO
LD MyLIFO.COUNT
ST COUNT
LD MyLIFO.PREAD
ST PREAD
LD MyLIFO.PWRITE
ST PWRITE