Coroutines are excellent for encoding state machines. See http://eli.thegreenplace.net/2009/08/29/co-routines-as-an-alternative-to-state-machines/

coroutines_vs_state_machines.rb

# Encoding: UTF-8
#
require 'fiber'

# This accepts generated frames and prints them.
#
target = Fiber.new do
  loop do
    frame = Fiber.yield
    puts "Frame received: #{frame}."
  end
end
target.resume

# This decodes frames and transfers control to the return value of the
# first yield, which should be a fiber that handles results.
#
def decoder_with_options options = {}
  header    = options[:header] || 0x61
  footer    = options[:footer] || 0x62
  dle       = options[:dle]    || 0xAB
  after_dle = options[:after_dle] || (->(x) { x.to_s(16) })
  payload   = options[:payload]   || (->(x) { x.to_s(16) })
  
  Fiber.new do |target|
    loop do
      part = Fiber.yield
      frame = ''
    
      if part == header
        loop do
          part = Fiber.yield
        
          case part 
            when footer
              target.resume frame
              break
            when dle
              part = Fiber.yield
              frame += after_dle[part]
          else
            frame += payload[part]
          end
        end
      end
    end
  end
end


decoder = decoder_with_options header: "61",
                               footer: "62",
                               dle: "AB",
                               after_dle: ->(x) { x },
                               payload: ->(x) { x }
decoder.resume(target)

["70", "24",
 "61", "99", "AF", "D1", "62",
 "56", "62",
 "61", "AB", "AB", "14", "62",
 "7"].each do |thing|
  decoder.resume thing
end


decoder = decoder_with_options
decoder.resume target

[0x70, 0x24,
 0x61, 0x99, 0xAF, 0xD1, 0x62,
 0x56, 0x62,
 0x61, 0xAB, 0xAB, 0x14, 0x62,
 0x7].each do |byte|
  decoder.resume byte
end


parts = [0x70, 0x24,
 0x61, 0x99, 0xAF, 0xD1, 0x62,
 0x56, 0x62,
 0x61, 0xAB, 0xAB, 0x14, 0x62,
 0x7]
 
100.times { decoder.resume parts.sample }