Single- or Multinode Data Communications
Single-Node (RS232) Communications
Each 4000 instrument's 9-pin Computer Interface Port permits full-handshake RS232 data interchanges of up to 153.6K baud with a host computer, PLC, printer, recorder, or other RS232 device. In this mode of operation, a supervisory computer can control the unit completely via simple ASCII mnemonic commands.
Depending on the application requirements, a 4000 instrument can be commanded by the operator or computer to output data from its Interface Port for one, all, or a selected range of channels, as retrieved from the instrument's continuously updated DATA RAM.
Time-coherent data "snapshot" transmissions are possible when you need to eliminate time skew within a data set. In this case, all or selected data values remain frozen until the transfer is complete.
An intertransmission delay of up to 0.1 second can be invoked to avoid overrunning the computer input buffer when full handshake protocols are not observed. Any user-entered "message" of up to 32 ASCII characters can also be transmitted on command from the Interface Port. Optional output formatting includes columns, channel-number "echo," and channel limit-zone indication.
Multinode (RS485 Network) Communications
When a 4000 unit is equipped with the "N" Option, its Interface Port can be configured for either "single-node" (RS232) or "multinode" (RS485) communications.
In multinode operation, the 4000 instrument can be a member of a high-speed multidrop network of up to 99 "N"-Option 4000 Series data-collection instruments, mixed as desired. For an example of a plant-wide 4000 network.
Network interchanges take place over simple twisted-pair RS485 "daisy-chain" linkage, at standard baud rates from 300 through 153.6K.
In a multinode network like the one shown above, the host computer can "open" any selected node by issuing an OPEN (OPN) command to the entire network. Only one node can be "open" at any one time. The currently "open" node (only) will respond to all subsequent commands issued to the network—including all requests for "local" measured and/or calculated data.
Simple polling routines let your computer optimize network transfer speed as it interrogates a sequence of nodes and receives appropriate response inputs.