MagTek MCP - Manual (Page 7)

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SECTION 1. OVERVIEW
This document describes the common format of the serial transport frames and defines the
protocol for using these frames.
This protocol can work as is with a RS-232 interface. However, the protocol needs to be adapted
slightly to work with a USB interface. The USB section of this document explains how to adapt
this protocol to work with a USB interface.
Since this protocol is rather complicated and time consuming to implement, newer devices
(introduced in 2006 - 2007) now have properties that can be adjusted to greatly simplify the
protocol and to make it easier to implement. Additionally, an alternative simple ASCII hex
protocol has been added. See the Host communications application section of the device
command reference manual for more information on these options. These options apply to both
the RS-232 and USB interfaces. It is highly recommended that the Host communications
application section of the device command reference manual is read prior to reading this
document any further because it may not be necessary to read this entire document if an
alternative protocol is chosen.
The protocol begins after two nodes are synchronized with each other. The main characteristics
of the protocol are the following:
• Nodes may send frames at any time, not only in response to a frame received from the
host. This makes the protocol symmetrical: the protocol is the same for the host and
for the device.
• A frame is the smallest data unit which can be exchanged between two nodes. A
frame may be used to convey:
a. application data transparent to the protocol
b. transmission control information including transmission error handling
• The frame format allows a node to validate the received frame before processing the
conveyed data (by using EDCs – error detection codes)
The serial transport protocol applies the principle of the layering of the OSI (Open System
Interconnection) reference model. Two layers are defined:
• Physical layer: transmits data organized into single characters
• Data-link layer: exchanges frames according to the rules defined in this chapter, this
also includes error handling and error recovery
This document defines the frame formats used in the protocol and defines the protocol rules used
for safe frame transmission, error handling and error recovery. At the end of the document,
scenarios are presented that clarify how the protocol is used in various situations.