Phocus Systems, Inc.

Digital PC Remote I/O Controller


Description:

The remote I/O cards provide a means to serially connect the host computer to external devices ( switches, photoeyes, limit switches, relays, etc.). A simple 4-wire RS422 connection is used for serial communication. Three different messages are available to the computer:
  • Who are you? message. The card returns its address and what type of card it is. This makes it easy to see which addresses are being used and what type of cards are being used.
  • Send output data message. The card updates the outputs and returns the address, outputs, and inputs.
  • Read data message. The card returns the address, outputs, and inputs.
The remote I/O card is replaceable without removing wires or setting jumpers. The card plugs into a wiring base (p.n. 1593) mounted on a standard din rail. The base contains screw terminals for the wires and contains jumpers for selecting the card address and RS422 terminators. Two sets of power and RS422 connections make daisy-chaining easier. Two captive screws hold the card to the base.

Communication:

The I/O cards only respond to messages sent by the computer. Three messages are available (request card type, send new output, request current data). Each computer message has the following format:
  • preamble - 3 bytes of all ones ( FFh, FFh, FFh ).
  • code/address - 1 byte ( msb c,c, a,a,a,a,a,a lsb ) .
  • data - 1 byte ( if needed ).
  • Communication is 8 bit, no parity, 1 stop bit, 115.2 kBaud.

Request Card Type message (4 bytes).

The computer requests the type of card for this address. If it is a 1592B I/O card, it responds with the code/address and the type number 9.
From computer (4 bytes) -- FFh, FFh, FFh, ( 1 0 a a a a a a ).
Card response (2 bytes) -- ( 1 0 a a a a a a ), 09h.

Send New Output Message (5 bytes).

The computer sends new output data to the card. The card updates the output relays and responds with the code/address and the current output data and the current input data.
From computer (5 bytes) -- FFh, FFh, FFh, ( 0 0 a a a a a a ), output.
Card response (3 bytes) -- ( 0 0 a a a a a a ),output, input .

Request Current Data Message(4 bytes).

The computer requests the current data from the card. The card responds with the code/address and the current output data and current input data. No change to the output relays will occur.
From computer (4 bytes) -- FFh, FFh, FFh, ( 0 1 a a a a a a ).
Card response (3 bytes) -- ( 0 1 a a a a a a ),output, input .
Communication from the computer can be continuous. The next card request message can be tacked onto the end of the current request message and so on. In this manner, data can be sent and received at a rate of one card every 434 micro seconds. The response from each card begins as soon as the address is received.

Connections:

There are 4 different types of connections to the card wiring base:
  • Power.
  • RS422 communications.
  • Output signals.
  • Input signals.

Power connections

Two sets of power connections are provided. This makes it easy to route power to the next card and so on. The three signals are:
  • DC+ ( from +7 to +40 VDC ).
  • DC- ( connected to earth ground ).
  • GND ( earth ground ).

RS422 communications connections

Two sets of communication connections are provided. This makes it easy to route the communications to the next card and so on. The five signals are:
  • RXA (RX-). The negative differential receive line from the computer.
  • RXB (RX+). The positive differential receive line from the computer.
  • TXY (TX-). The negative differential transmit line to the computer.
  • TXZ (TX+). The positive deferential transmit line to the computer.
  • SHIELD.

Output connections

The 1592B I/O card uses normally open contacts for output signals. Both sides of the contact are provided for each output. The base contains 0.5 amp fuses for each of the 9 outputs. 8 outputs are for data and one output is for communication status.
The communication status signal is active as long as the computer keeps addressing the card at least every two seconds. The contacts will open within two seconds if communication stops. This signal can be used to detect if the computer is on line and take appropriate action if it is not.

Input Connections

There are 8 optically isolated inputs. Each input provides access to both the positive and negative sides of the isolator. Thus the inputs can individually be connected to active high or active low signals. The input will be on for voltage differences from 5 to 40 VDC.

Jumpers:

There are three sets of jumpers on the 1593B wiring base (not on the I/O card). One set is used to program the address of the card. One set is used to terminate the RS422 communication lines (last card). One set is used to isolate grounds or jumper grounds together.

Address Jumpers ( 3Fh is not valid )

Six jumper positions are used to create an address from 0 to 62 (3Eh). 63 is an invalid address. The card will not respond to address 63. Installing a jumper is equivalent to setting that address bit to a 1.

RS422 Termination Jumpers

The last card on the communications line should be terminated with 120 ohm resistors across the differential pairs. The rest of the cards should not be terminated. These resistors are already on the wiring base and can be used or removed by using the termination jumpers.

Ground Jumpers

Depending on your system design, you may wish to connect grounds together at each wiring card or you may want them kept separate. One jumper is used to connect the DC- signal to GND. The other jumper connects the RS422 shield to GND.

Sample Remote IO Wiring Diagram - click to enlarge Remote IO Wiring Base - click to enlarge
Remote IO Input Connections - click to enlarge Remote IO Output Connections - click to enlarge

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This product is a member of the PC Remote I/O Family.



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Phocus Systems Inc.
P.O. Box 16160
Seattle, Washington 98116
Tel: (206) 972-0931
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