--- a/lib/bistable.txt	Mon Apr 04 11:19:48 2011 +0100
+++ b/lib/bistable.txt	Mon Apr 04 14:32:21 2011 +0100
@@ -1,21 +1,28 @@
 (*
- * (c) 26 Feb 2001 David Campbell
+ *  matiec - a compiler for the programming languages defined in IEC 61131-3
  *
- * Offered to the public under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2 of the
- * License, or (at your option) any later version.
+ *  Copyright (C) 2011  Mario de Sousa (msousa@fe.up.pt)
  *
- * 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.
+ *  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 IL and ST compiler.
+ * An IEC 61131-3 compiler.
  *
  * Based on the
  * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
@@ -31,35 +38,42 @@
  * -------------------------
  *)
 
+(* The standard defines the SR FB thus: 
+
+                  +-----+
+S1----------------| >=1 |---Q1
+         +---+    |     |
+ R------O| & |----|     |
+ Q1------|   |    |     |
+         +---+    +-----+
+*)
 
 FUNCTION_BLOCK SR
   VAR_INPUT
-    S1 : BOOL;
-    R  : BOOL;
+    S1, R : BOOL;
   END_VAR
   VAR_OUTPUT
     Q1 : BOOL;
   END_VAR
-  VAR
-    Q_INTERNAL : BOOL;
-  END_VAR
+  Q1 := S1 OR ((NOT R) AND Q1);
+END_FUNCTION_BLOCK
 
-  Q_INTERNAL := S1 OR ( Q_INTERNAL AND (NOT R));
-  Q1 := Q_INTERNAL;
-END_FUNCTION_BLOCK
+
+(* The standard defines the RS FB thus: 
+                   +---+
+R1----------------O| & |---Q1
+        +-----+    |   |
+S-------| >=1 |----|   |
+Q1------|     |    |   |
+        +-----+    +---+
+*)
 
 FUNCTION_BLOCK RS
   VAR_INPUT
-    S : BOOL;
-    R1 : BOOL;
+    S, R1 : BOOL;
   END_VAR
   VAR_OUTPUT
     Q1 : BOOL;
   END_VAR
-  VAR
-    Q_INTERNAL : BOOL;
-  END_VAR
-
-  Q_INTERNAL := (NOT R1) AND (S OR Q_INTERNAL);
-  Q1 := Q_INTERNAL;
+  Q1 := (NOT R1) AND (S OR Q1);
 END_FUNCTION_BLOCK