Omega A2400 manual Do, Oc, Cc, Rd, Rea, Rid, Rlp, Rs, Rsp, Rsu

Communication 3-2

improper command prompt or address is transmitted. The table below lists the timeout specification for each command assuming that delay times T1, T2, T3 = 0:

Table 3.1 Response Timeout Specifications.
Mnemonic	Timeout
DO, OC, CC, RD, REA, RID, RLP, RS, RSP, RSU,	≤ 10 ms
RT1, RT2, RT3, WE	≤ 100 ms
EA, ID, LP, RID, RR, SP, SU, T1, T2, T3

The timeout specification is the turn-around time from the receipt of a command to when the module starts to transmit a response.

Data Format

All A2400 modules communicate in standard NRZ asynchronous data format. This format provides one start bit, seven data bits, one parity bit and one stop bit for each character.

RS-485

RS-485 is a recently developed communications standard to satisfy the need for multidropped systems that can communicate at high data rates over long distances. RS-485 is similar to RS-422 in that it uses a balanced differential pair of wires switching from 0 to 5V to communicate data. RS-485 receivers can handle common mode voltages from -7V to +12V without loss of data, making them ideal for transmission over great distances. RS-485 differs from RS-422 by using one balanced pair of wires for both transmitting and receiving. Since an RS-485 system cannot transmit and receive at the same time it is inherently a half-duplex system. RS-485 offers many advantages over RS-232:

1)balanced line gives excellent noise immunity

2)can communicate with modules at 38400 baud

3)communications distances up to 10,000 feet.

4)true multidrop; modules are connected in parallel

5)individual modules may be disconnected without affecting other modules

6)up to 32 modules on one line; 124 with repeaters

7)no communications delay due to multiple modules

8)simplified wiring using standard telephone cable

An RS-485 system usually requires an interface such as the A2400 to convert RS-232 to RS-485.