(*
 *  matiec - a compiler for the programming languages defined in IEC 61131-3
 *
 *  Copyright (C) 2011  Mario de Sousa (msousa@fe.up.pt)
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * This code is made available on the understanding that it will not be
 * used in safety-critical situations without a full and competent review.
 *)

(*
 * An IEC 61131-3 compiler.
 *
 * Based on the
 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
 *
 *)


(*
 * This is part of the library conatining the functions
 * and function blocks defined in the standard.
 *
 * SR and RS function blocks
 * -------------------------
 *)

(* The standard defines the SR FB thus: 

                  +-----+
S1----------------| >=1 |---Q1
         +---+    |     |
 R------O| & |----|     |
 Q1------|   |    |     |
         +---+    +-----+
*)

FUNCTION_BLOCK SR
  VAR_INPUT
    S1, R : BOOL;
  END_VAR
  VAR_OUTPUT
    Q1 : BOOL;
  END_VAR
  Q1 := S1 OR ((NOT R) AND Q1);
END_FUNCTION_BLOCK


(* The standard defines the RS FB thus: 
                   +---+
R1----------------O| & |---Q1
        +-----+    |   |
S-------| >=1 |----|   |
Q1------|     |    |   |
        +-----+    +---+
*)

FUNCTION_BLOCK RS
  VAR_INPUT
    S, R1 : BOOL;
  END_VAR
  VAR_OUTPUT
    Q1 : BOOL;
  END_VAR
  Q1 := (NOT R1) AND (S OR Q1);
END_FUNCTION_BLOCK