--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mb_util.h	Sun Mar 05 00:05:46 2017 +0000
@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2002,2016 Mario de Sousa (msousa@fe.up.pt)
+ *
+ * This file is part of the Modbus library for Beremiz and matiec.
+ *
+ * This Modbus library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser 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 Lesser 
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this Modbus library.  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.
+ */
+
+
+
+#ifndef MB_UTIL_H
+#define MB_UTIL_H
+
+/* This file has constants related to the modbus protocol */
+/*
+ * Some of these constants are specific to the layer two protocols
+ * (i.e. master and slave), while others are specific of the
+ * layer one protocols (i.e. rtu, ascii, tcp).
+ *
+ * a) Unfortunately, due to the nature of the modbus protocol, that does not
+ * include a frame size field in the layer 1 frame (see note 1), and the
+ * fact that we are implementing it at the user level, the implementation
+ * of some layer 1 protocols need to know the content of the layer 2 protocol
+ * in order to determine the size of the frame.
+ *
+ * b) The layer two message formats are in fact the same, just reversing the role
+ * being played (master or slave).
+ *
+ * Bothe a) and b) mean we need the same modbus protocol constants in several files.
+ * It ends up making more sense to put them all together in a single file, which
+ * makes updating easier, even though we are trying to strictly seperate the layer 1
+ * and layer 2 protocols.
+ *
+ *
+ *
+ * Notes:
+ *  (1) There is no layer 1 field with the frame size, nevertheless this
+ *      size can be determined indirectly due to timing restrictions on the rtu
+ *      protocol. Unfortunately, due to the fact that we are implementing
+ *      it at the user level, we are not guaranteed to detect these timings
+ *      correctly, and therefore have to rely on layer 2 protocol info to
+ *      determine the frame size.
+ *      For the ascii protocol, the frame size is determined indirectly by
+ *      a frame header and tail, so we do not use layer 2 protocol info.
+ */
+
+
+ /* Layer 2 Frame Structure...                */
+ /* Valid for both master and slave protocols */
+#define L2_FRAME_HEADER_LENGTH    6
+#define L2_FRAME_BYTECOUNT_LENGTH 1
+#define L2_FRAME_DATABYTES_LENGTH 255
+#define MAX_L2_FRAME_LENGTH (L2_FRAME_HEADER_LENGTH + L2_FRAME_BYTECOUNT_LENGTH +    \
+                             L2_FRAME_DATABYTES_LENGTH)
+
+#define L2_FRAME_SLAVEID_OFS    0
+#define L2_FRAME_FUNCTION_OFS   1
+
+ /* Layer 1 - Ascii Frame sizes... */
+#define L2_TO_ASC_CODING        2 /* number of ascii bytes used to code a Layer 2 frame byte */
+#define ASC_FRAME_HEADER_LENGTH 1
+#define ASC_FRAME_HEADER        ':'
+#define ASC_FRAME_TAIL_LENGTH   2
+#define ASC_FRAME_TAIL_0        '\13' /* 'CR' */
+#define ASC_FRAME_TAIL_1        '\10' /* 'LF' */
+#define ASC_FRAME_LRC_LENGTH    2
+
+ /* Layer 1 - RTU Frame sizes... */
+#define RTU_FRAME_CRC_LENGTH    2
+
+ /* Layer 1 - TCP Frame sizes... */
+#define TCP_HEADER_LENGTH       6
+
+ /* Global Frame sizes */
+#define MAX_RTU_FRAME_LENGTH MAX_L2_FRAME_LENGTH + RTU_FRAME_CRC_LENGTH
+#define MAX_ASC_FRAME_LENGTH ((MAX_L2_FRAME_LENGTH * L2_TO_ASC_CODING) +             \
+                              ASC_FRAME_HEADER_LENGTH + ASC_FRAME_TAIL_LENGTH +      \
+                              ASC_FRAME_LRC_LENGTH)
+                              
+
+/* Modbus Exception codes */
+#define ERR_ILLEGAL_FUNCTION                        0x01
+#define ERR_ILLEGAL_DATA_ADDRESS                    0x02 
+#define ERR_ILLEGAL_DATA_VALUE                      0x03 
+#define ERR_SLAVE_DEVICE_FAILURE                    0x04 
+#define ERR_ACKNOWLEDGE                             0x05 
+#define ERR_SLAVE_DEVICE_BUSY                       0x06 
+#define ERR_NEGATIVE_ACKNOWLEDGE                    0x07 
+#define ERR_MEMORY_PARITY_ERROR                     0x08 
+#define ERR_GATEWAY_PATH_UNAVAILABLE                0x0A 
+#define ERR_GATEWAY_TARGET_DEVICE_FAILED_TO_RESPOND 0x0B 
+
+
+
+#endif  /* MB_UTIL_H */
+
+
+
+
+
+
+
+