dbx full_duplex_data_link - Manual

Full Duplex Transport Layer Specification Page 1 of 5
ZonePRO Full Duplex Network and Data Link Layer Specification
Author: John Lee
Creation Date: January 7, 2004
Revision:
1.0
Last Edit Date: April 27, 2004
Description:
Data Link and Network Layer specification for full duplex point-to-point
communication
1. Overview
This document outlines the Harman International data link and network layers for full duplex 232 or 485
point to point links .
2. Physical Layer (PHY)
This section defines the physical layer specification, including signaling, terminations, DC biasing, and
ground isolation.
2.1. Encoding
Data is transmitted NRZ encoded, LSB first as is shown below:
We refer to a logic 1 as a mark, a logic 0 as a space to conform with the RS-232 specification.
A stop bit is provided after each transmitted byte of data and is used for guarantee a falling edge on the
next start bit. A stop condition is mark for one bit interval and will be present after each framing bit.
Bits 7 through 0 represent the transmitted data.
The falling edge of the start bit is used to sync the UART to the beginning of the transmitted byte.
2.2. Baud Rate
The following baud rates can be supported by the DriveRack RS-232 and RS-485 full duplex data link
layers: 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200.
2.3. Breaks and Line Faults
Breaks are considered a violation of the protocol and should force a resync if received.
2.4. Flags
Flags may be passed between the stations to mark layer events. A flag is a single byte sent between
frames. The following flags are defined:
Flags
Flag Value Function
ACK A5h Sent on positive receipt of a frame send via guaranteed
delivery.
NAK DAh Sent on negative receipt of a frame send via guaranteed
delivery.
Ping 8Ch Send by station if no activity is present. Used to detect loss of
link.
Resync Request FFh Send by a receiving station if it believes its out of sync with the
sending station.
Resync Acknowledgement F0h Send by a station after receiving a Resync Request flag.