Apollo IMY 20 mA CURRENT LOOP SERIAL COMMUNICATIONS(Optional)

20 mA CURRENT LOOP SERIAL COMMUNICATIONS(Optional)

Theserial communication option is a half-duplex, two-way, 20 mA loop

thatcan connect to a variety of printers, computers, terminals and controllers

tosuit many data-polling or automatic operation applications. The indicator

respondsto a host of commands, including change alarm value, reset totalizer

andtransmit input value. Two loops are required for all hook-ups; a transmit

(out-goingdata) loop and a receive (in-coming data) loop. Since the indicator

monitors the receive loop for a busy signal (current interrupted) while

transmitting, the receive loop must be connected even if the indicator is

transmittingonly, such as to a printer. A built-in 20 mA source can be used in

the transmit loop (only) by connecting the current return wire to -20 mA

SRC.,instead of SO+. To bypass the built-in current source, make transmit

loopconnections to SO+ and SO-. Additionally, multiple units and other Red

LionControls instruments can be serially addressed, up to a maximum of 99

units.(The actual number in a single loop is limited by the serial hardware

specifications.)To eliminate problems with ground loops, the serial circuitry

isisolated from both signal common and output common. Optional 20 mA to

RS232Cand20 mA to RS422 converter modules expand the unit’s flexibility.

Note:When operating the unit with a printer, the receive loop of the indicator

musthave current flowing into it before transmission can take place.

Datais sent by switching current on and off in the loop and is received by

monitoring the switching action and interpreting the codes that are

transmitted. In order for data to be correctly interpreted, there must be

identicalformats and baud rates among the communicating equipment. The

onlyformat available with this indicator is 1 start bit, 7 data bits, 1 odd parity

bitand 1 stop bit. The baud rates are programmable and the choices are: 300,

600,1200 and 2400.

Before serial communication can take place, the indicator must be

programmedto the same baud rate as the connected equipment. In addition, the

loopaddress number, print options and full or abbreviated transmission must

beprogrammed. If only one indicator is to be used, then a loop address number

of“0” may by used, to eliminate the requirement for the address specifier when

sendinga command. If more than one indicator is on the loop, assignment of

uniqueaddresses, other than zero, for each indicator is recommended. Valid

addressesof 0 to 99 may be assigned, but the built-in current source, if used, is

capableof driving up to 7 units. Additional drive capability may be afforded by

an external current source with a higher compliance voltage. Refer to

programmingsection “Pro 7” to program the serial option.

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DATAFORMAT-10 BIT FRAME [300, 600, 1200, 2400 Baud]