FIFO
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 |
IN | ANY | Value to be pushed |
@Tail | ANY | Value of the oldest pushed value - updated after call! |
Buf[] | ANY | Array for storing values |
Outputs
EMPTY | BOOL | TRUE if the list is empty |
OFLO | BOOL | TRUE if overflow on a PUSH command |
Count | DINT | Number of values in the list |
pRead | DINT | Index in the buffer of the oldest pushed value |
pWrite | DINT | Index in the buffer of the next push position |
Remarks
IN, @Tail and Buf[] must have the same data type and cannot be STRING.
The @Tail argument specifies a variable which is filled with the oldest push value after the block is called.
Values are stored in the "BUF" array. Data is arranged as a roll over buffer and is never shifted or reset. Only read and write pointers and pushed values are updated. The maximum size of the list 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 BUF input, the call is considered as invalid and makes nothing. Outputs reports an empty list in this case.
In FFLD language, input rung is the PUSH input. The output rung is the EMPTY output.
ST Language
(* MyFIFO is a declared instance of FIFO function block *)
MyFIFO (PUSH, POP, RST, IN, @Tail , BUFFER);
EMPTY := MyFIFO.EMPTY;
OFLO := MyFIFO.OFLO;
COUNT := MyFIFO.COUNT;
PREAD := MyFIFO.PREAD;
PWRITE := MyFIFO.PWRITE;
FBD Language
FFLD Language
IL Language
(* MyFIFO is a declared instance of FIFO function block *)
Op1: CAL MyFIFO (PUSH, POP, RST, IN, @Tail , BUFF[])
FFLD MyFIFO.EMPTY
ST"Structured text" A high-level language that is block structured and syntactically resembles Pascal EMPTY
FFLD MyFIFO.OFLO
ST OFLO
FFLD MyFIFO.COUNT
ST COUNT
FFLD MyFIFO.PREAD
ST PREAD
FFLD MyFIFO.PWRITE
ST PWRITE
See also