dbx full_duplex_data_link - Manual (Page 2)

Full Duplex Transport Layer Specification Page 2 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
± 3V into an
impedance varying from 3k Ω to 7kΩ at the receiving device. The transmitting device must
guarantee that it will provide from ± 5V to ± 15V at the receiver. The receiver must be able to
tolerate open circuit voltages up to 25V. A mark is defined as a negative potential, a space as a
positive potential.
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 100
Ω 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 100
Ω 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