dbx full duplex User Manual

ZonePRO Full Duplex Network and Data Link Layer Specification

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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:

John Lee
January 7, 2004

1.0
April 27, 2004

Data Link and Network Layer specification for full duplex point-to-point
communication

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.

Full Duplex Transport Layer Specification Page 1 of 5

2.5. Ping

To detect a loss of communication between host and DriveRack, each unit will issue a ping should no
activity occur for a period of 2 seconds (smaller ping intervals are also acceptable). If no ping is
received within 4 seconds, a resync should be issued.

2.6. Resync

To provide a mechanism to resync, either unit may issue a network resync. A resync is a stream of
Resync Request flags.

On reception of a resync, the receiving station should respond with a continuous stream of at least 261
Resync Acknowledgement flags.

As soon as a station detects a received resync request flag or resync acknowledge flag it should stop
transmission of resync request flags. Should a resync request be received during transmission of a
resync request, the receiving station should respond by sending at least 261 acknowledgements.

2.7. Interface Startup

Each station should startup using the resync protocol as outlined in section 2.6.

2.8. Signaling

2.8.1. RS-232

Signaling for the RS-232 interface will comply with the RS-232E specification. The RS-232
specification is an unbalanced transmission format requiring a signal swing of
impedance varying from 3kΩ to 7kΩ at the receiving device. The transmitting device must
guarantee that it will provide from

tolerate open circuit voltages up to 25V. A mark is defined as a negative potential, a space as a
positive potential.

±5V to ±15V at the receiver. The receiver must be able to

± 3V into an

2.8.2. RS-485

Signaling for the RS-485 interface will comply with the EIA-485 standard. EIA-485 (also called
RS-485) is a balanced transmission format with two signals, B and A. Logic 1 will be represented
by B-A > 100mV. Logic 0 will be represented by B-A < -100mV. Receivers will be less than 1
unit load as defined by the EIA-485 specification and will have at least 50mV of hysteresis to
provide noise immunity.

2.9. Mechanical

2.9.1. RS-232

2.9.2. RS-485

2.10. Terminations and Biasing

2.10.1. RS-485

A 100Ω parallel termination will be provided at each transmitter and receiver. Biasing networks
should also be provided at each receiver (termination resistor should be adjusted at the receiver to
provide a 100Ω effective termination).

2.11. Ground Isolation
Due to the DC offset that exists in NRZ encoded bitstreams, and the complexity involved in designing
wettable transformers to operate over a fairly wide range of source/load impedances, ground isolation

Full Duplex Transport Layer Specification Page 2 of 5