Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication17
{
    class Program
    {
        static void Main(string[] args)
        {
            string text = "0T011.35000000OKAPPROVEDCVI406000000025701601100000000099901122201TEST/BLUEFIN03120160801150802CARDBIN=412493#";

            using (StringReader reader = new StringReader(text))
            using (CommandReader commandReader = new CommandReader(reader))
            {
                commandReader.Read();

                var t01 = commandReader.Command.ToT01();
                Console.WriteLine(new { t01.Amount });
            }
        }
    }

    class T01Command
    {
        public decimal Amount { get; set; }
    }

    static class CommandExtensions
    {
        public static T01Command ToT01(this Command command)
        {
            T01Command t01 = new T01Command();

            // Ignore type.
            command.Fields.Dequeue();
            
            var field = command.Fields.Dequeue();
            t01.Amount = decimal.Parse(field.Value);

            return t01;
        }
    }

    class Command
    {
        public Command(int status)
        {
            Fields = new Queue<Field>();
            Status = status;
        }

        public Queue<Field> Fields { get; }
        public int Status { get; }
    }

    class Field
    {
        public Field(string value)
        {
            Units = new Queue<string>();
            Value = value;
        }

        public Queue<string> Units { get; }
        public string Value { get; }

        public override string ToString() => Value;
    }

    class CommandReader : IDisposable
    {
        TextReader reader;
        CommandReaderState state;

        public CommandReader(TextReader reader)
        {
            this.reader = reader;
        }

        public Command Command { get; private set; }

        public void Read()
        {
            int position = 0;
            char[] buffer = new char[80];
            int read;

            const char stx = '\x02';
            const char fs = '\x1c';
            const char us = '\x1f';
            
            StringBuilder field = new StringBuilder();
            StringBuilder unit = new StringBuilder();
            int statusStart = -1;
            while ((read = reader.ReadBlock(buffer, position, buffer.Length)) > 0)
            {
                for (int i = 0; i < buffer.Length;)
                {
                    char c = buffer[i];
                    switch (state)
                    {
                        case CommandReaderState.None:
                            if (c == stx) { state = CommandReaderState.Status; }
                            if (c == fs) { state = CommandReaderState.BeginField; }

                            i++;
                            break;
                        case CommandReaderState.Status:
                            if (statusStart == -1) { statusStart = i; }

                            if (c == fs)
                            {
                                int status = int.Parse(new string(buffer, statusStart, i - statusStart));
                                Command = new Command(status);
                                state = CommandReaderState.BeginField;
                            }

                            i++;
                            break;
                        case CommandReaderState.BeginField:
                            if (unit.Length > 0)
                            {
                                Command.Fields.Peek().Units.Enqueue(unit.ToString());
                            }
                            unit.Clear();
                            if (field.Length > 0)
                            {
                                Command.Fields.Enqueue(new Field(field.ToString()));
                            }
                            field.Clear();
                            state = CommandReaderState.Field;
                            break;
                        case CommandReaderState.Field:
                            if (c == fs) { state = CommandReaderState.BeginField; }
                            else if (c == us) { state = CommandReaderState.BeginUnit; }
                            else { field.Append(c); }

                            i++;
                            break;
                        case CommandReaderState.BeginUnit:
                            if (unit.Length > 0)
                            {
                                Command.Fields.Peek().Units.Enqueue(unit.ToString());
                            }
                            unit.Clear();
                            state = CommandReaderState.Unit;
                            break;
                        case CommandReaderState.Unit:
                            if (c == fs) { state = CommandReaderState.BeginField; }
                            else if (c == us) { state = CommandReaderState.BeginUnit; }
                            else { unit.Append(c); }

                            i++;
                            break;
                    }
                }
            }
        }

        public void Dispose()
        {
            ((IDisposable)reader).Dispose();
        }

        enum CommandReaderState
        {
            None,
            Status,
            BeginField,
            Field,
            BeginUnit,
            Unit
        }
    }
}