OPTO 22 Optomux B1, Руководство пользователя

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CHAPTER 2: INTRODUCTION
B1 and B2 User’s Guide
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Wiring
Inputs and outputs are connected to the Optomux mounting rack via an industrial barrier strip with
integral cable clamp for each terminal. Spade lugs, other wire terminations, bare wires, and tinned
wires are all readily accepted. Serial link connections and power connections are also made via
screw terminals.
Data Transmission
Optomux supports 8 baud rates (300, 600, 1,200, 2,400, 4,800, 9,600, 19.2K, and 38.4K) which are
selectable via jumpers located on the Optomux unit. Selection of baud rate often depends upon the
capabilities of the host port. Many host computers are limited to 9,600. Modems and radio links
usually operate at either 300 or 1,200 baud. System throughput is increased by using the fastest
available baud rate.
Optomux is capable of using two types of message protocols. The 2-pass protocol is intended for
use during normal operation. This protocol requires the transmission of two messages on the serial
link every time a command is executed. The host sends a command to an Optomux unit and then
receives a response message acknowledging successful execution of the command along with any
requested data, or an error message indicating that the Optomux detected an error in the command
message and was unable to execute it.
A 4-pass protocol is also available. This protocol is sometimes useful during initial setup and
installation because it allows the host to examine and display the command message that Optomux
received. The command message is echoed back to the host by Optomux for verification, before it
can be executed. After the host verifies that the two messages are identical, an execute command
gives Optomux the go ahead, the required action is performed, and any requested data is returned.
To ensure secure data transmission, every Optomux command message, and every response from
Optomux which contains data, includes a calculated checksum. Optomux never executes a
command containing a checksum error.
System Throughput
In most control applications, some points need to be updated more frequently than others. This
section will help you estimate the minimum timing between successive events or transactions.
The total time required to complete an Optomux instruction is approximately equal to the
transmission time of all the characters in the instruction, plus all the characters in the response. The
time required for digital Optomux units to respond to a command is typically less than 1
millisecond. Typical analog Optomux response times are from 3 to 7 milliseconds.
A total of 15 characters are required to read the ON/OFF status of all 16 positions on a digital
Optomux unit. The command sent from the host requesting the status consist of 7 characters; the
response from Optomux consists of 8 characters. The following table shows system throughput,
assuming that it takes 1 millisecond for Optomux to respond to the host command.
Reading the values of 16 analog inputs on an analog Optomux unit requires a total of 79
command/response characters. The command sent by the host consists of 11 characters; the
response from Optomux consists of 68 characters. If we assume a response time of 7 milliseconds,
the following table shows system throughput based upon reading all 16 positions per transaction.