LIFO
Inputs
PUSH | BOOL | Push a new value (on rising edgeA rising edge is the transition of a digital signal from low to high. It is also called positive 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 |
Outputs
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 |
Remarks
NEXTIN, NEXTOUT and BUFFER must have the same data type and cannot be STRING. The NEXTOUT argument specifies a variable which 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 FFLD language, input rung is the PUSH input. The output rung is the EMPTY output.
ST Language
(* 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;
FBD Language
FFLD Language
IL Language
(* MyLIFO is a declared instance of LIFO function block *)
Op1: CAL MyLIFO (PUSH, POP, RST, NEXTIN, NEXTOUT, BUFFER)
FFLD MyLIFO.EMPTY
ST"Structured text" A high-level language that is block structured and syntactically resembles Pascal EMPTY
FFLD MyLIFO.OFLO
ST OFLO
FFLD MyLIFO.COUNT
ST COUNT
FFLD MyLIFO.PREAD
ST PREAD
FFLD MyLIFO.PWRITE
ST PWRITE
See also