The 3964R protocol (also referred to as DUST) provides the link layer
functionalities, so it is not a fully functional protocol in a proper sense.
It supports transparent transmission of data blocks on point-to-point
connections, operating in half-duplex mode.
The physical layer operates in asynchronous standard mode (1 start bit, 8
data bits, 1 parity and 1 stop bit) using the ISO 7 bit character code for
control commands (such as DLE, STX, ETX).
There are two variants::
- 3964
only parity is used to ensure data integrity
- 3964R
in addition, horizontal parity is used to ensure data integrity
The protocol has been very popular in process automation, in particular for
data exchange between devices with Simatic-SPS. 3964R is also used as link
layer for a Sinaut 8FW variant.
