Page 4 NDA-30115 Revision 1.0
Architecture Property Management System - Communication Interface
Asynchronous Transmission

Line Control

Characteristics The characteristics of the signal s transmitted acro ss the communications l ink are as
follows:
Table 2-1 Line Control Characteristics
Item Conditions
Control Method Contention method (point to point)
Operating Mode Half duplex (if modems are used, set to full duplex)
Synchronization Start-stop system
Data Rate 1200, 2400 or 4800 bits/second (bps)
Frame Contents ASCII (7bits)
Error Control Method VRC: Parity, LRC: BCC
Bit Transmission Order Priority is given to low order bits.
Transmission Intervals At each data generation. When a stream of information is
transmitted to the NEAX continuously, an interval of 0.5
seconds or more should be given between messages. Each
message must be delimited by the E OT code.
Priority Sequence Primary office: NEAX
Secondary Office: PMS
Stop bit 1 bit or 2 bits
Error Control VRC: Even, odd or no parity.
LRC: (BCC) Exclusive OR of the message text, starting after the
STX, and ending with (and including) the ETX.
Message Composition One message constitutes one record; SOH, TTB and ETB are not
used.
Message Length V ariable leng th, maximum of 128 charact ers (including STX and
ETX).
Electrical Interface EIA RS-232C electrical standard interface
Signal Form EIA RS-404
Interface Distance Maximum of 50 feet between the NEAX and the PMS when not
using a modem.
Word Framing 10 bits (1 start, 7 data, 1 parity, 1 stop) or 11 bits (1 start, 7 data,
1 parity, 2 stop)