View source for ISO Data Link Layer

The protocol is based on the '''ISO 1745''' standard using the ISO 1155 longitudinal parity. The protocol can be used with RS232 and RS422 pointtopoint connection, but also with RS485 multidrop bus connection. 

The ISO Data Link layer procedure is based on the ISO1745 standard: Information processing  Basic mode control procedures for data communication systems. The standard includes the concept of having a Control Device, Master Device and Slave Device.

The Control Device polls the devices, one at a time in an orderly fashion, inviting them to transmit messages. The devices that transmits a message becomes the Master Device. This device selects the destination device, which becomes the Slave Device, inviting it to receive an information message.  The Master Device sends the message and the Slave Device acknowledges the message.

The AlphaCom module is always the Control Device.


== Overview ==

A complete message transmission sequence progress as follows:
[[Image: ISO Data Link Layer Overview.jpg|left|400px|thumb|complete message transmission sequence]]


=== Transmission Control Characters used ===

[[ISO Data Link Layer_Overview_Transmission Control Characters used.jpg|left|300px|thumb]]