Add support for reading/writing the legacy DATE (IEC date) datatype

S7.Net/Enums.cs

@@ -202,6 +202,11 @@ public enum VarType
         /// DateTIme variable type
         /// </summary>
         DateTime,
+
+        /// <summary>
+        /// IEC date (legacy) variable type
+        /// </summary>
+        Date,
 
         /// <summary>
         /// DateTimeLong variable type

S7.Net/Helper/DateTimeExtensions.cs

@@ -0,0 +1,23 @@
+using System;
+using S7.Net.Types;
+using DateTime = System.DateTime;
+
+namespace S7.Net.Helper
+{
+    public static class DateTimeExtensions
+    {
+        public static ushort GetDaysSinceIecDateStart(this DateTime dateTime)
+        {
+            if (dateTime < Date.IecMinDate)
+            {
+                throw new ArgumentOutOfRangeException($"DateTime must be at least {Date.IecMinDate:d}");
+            }
+            if (dateTime > Date.IecMaxDate)
+            {
+                throw new ArgumentOutOfRangeException($"DateTime must be lower than {Date.IecMaxDate:d}");
+            }
+
+            return (ushort)(dateTime - Date.IecMinDate).TotalDays;
+        }
+    }
+}

S7.Net/PLCHelpers.cs

@@ -251,6 +251,15 @@ private static void BuildReadDataRequestPackage(System.IO.MemoryStream stream, D
                     {
                         return TimeSpan.ToArray(bytes);
                     }
+                case VarType.Date:
+                    if (varCount == 1)
+                    {
+                        return Date.FromByteArray(bytes);
+                    }
+                    else
+                    {
+                        return Date.ToArray(bytes);
+                    }
                 default:
                     return null;
             }
@@ -280,6 +289,7 @@ internal static int VarTypeToByteLength(VarType varType, int varCount = 1)
                 case VarType.Timer:
                 case VarType.Int:
                 case VarType.Counter:
+                case VarType.Date:
                     return varCount * 2;
                 case VarType.DWord:
                 case VarType.DInt:

S7.Net/Protocol/Serialization.cs

@@ -26,6 +26,11 @@ public static byte[] SerializeDataItem(DataItem dataItem)
                     _ => Types.String.ToByteArray(s, dataItem.Count)
                 };
 
+            if (dataItem.VarType == VarType.Date)
+            {
+                return Date.ToByteArray((System.DateTime)dataItem.Value);
+            }
+
             return SerializeValue(dataItem.Value);
         }
 

S7.Net/Types/Date.cs

@@ -0,0 +1,82 @@
+using System;
+using S7.Net.Helper;
+
+namespace S7.Net.Types
+{
+    /// <summary>
+    /// Contains the conversion methods to convert Words from S7 plc to C#.
+    /// </summary>
+    public static class Date
+    {
+        /// <summary>
+        /// Minimum allowed date for the IEC date type
+        /// </summary>
+        public static System.DateTime IecMinDate { get; } = new(year: 1990, month: 01, day: 01);
+
+        /// <summary>
+        /// Maximum allowed date for the IEC date type
+        /// <remarks>
+        /// Although the spec allows only a max date of 31-12-2168, the PLC IEC date goes up to 06-06-2169 (which is the actual
+        /// WORD max value - 65535) 
+        /// </remarks>
+        /// </summary>
+        public static System.DateTime IecMaxDate { get; } = new(year: 2169, month: 06, day: 06);
+
+        private static readonly ushort MaxNumberOfDays = (ushort)(IecMaxDate - IecMinDate).TotalDays;
+
+        /// <summary>
+        /// Converts a word (2 bytes) to IEC date (<see cref="System.DateTime"/>)
+        /// </summary>
+        public static System.DateTime FromByteArray(byte[] bytes)
+        {
+            if (bytes.Length != 2)
+            {
+                throw new ArgumentException("Wrong number of bytes. Bytes array must contain 2 bytes.");
+            }
+
+            var daysSinceDateStart = Word.FromByteArray(bytes);
+            if (daysSinceDateStart > MaxNumberOfDays)
+            {
+                throw new ArgumentException($"Read number exceeded the number of maximum days in the IEC date (read: {daysSinceDateStart}, max: {MaxNumberOfDays})", 
+                    nameof(bytes));
+            }
+
+            return IecMinDate.AddDays(daysSinceDateStart);
+        }
+
+        /// <summary>
+        /// Converts a <see cref="System.DateTime"/> to word (2 bytes)
+        /// </summary>
+        public static byte[] ToByteArray(System.DateTime dateTime) => Word.ToByteArray(dateTime.GetDaysSinceIecDateStart());
+
+        /// <summary>
+        /// Converts an array of <see cref="System.DateTime"/>s to an array of bytes
+        /// </summary>
+        public static byte[] ToByteArray(System.DateTime[] value)
+        {
+            var arr = new ByteArray();
+            foreach (var date in value)
+                arr.Add(ToByteArray(date));
+            return arr.Array;
+        }
+
+        /// <summary>
+        /// Converts an array of bytes to an array of <see cref="System.DateTime"/>s
+        /// </summary>
+        public static System.DateTime[] ToArray(byte[] bytes)
+        {
+            var values = new System.DateTime[bytes.Length / sizeof(ushort)];
+
+            for (int i = 0; i < values.Length; i++)
+            {
+                values[i] = FromByteArray(
+                    new[]
+                    {
+                        bytes[i], bytes[i + 1]
+                    });
+            }
+
+            return values;
+        }
+    }
+}