Optomux Applications FAQ

Q: What are the advantages of using an Optomux I/O system?

A: Optomux is a very cost-effective, powerful, modular system for monitoring and controlling moderate amounts of I/O. The serial data link, while not extremely fast, is very reliable, over distances up to 4,000 feet. Because the communications line can be shielded, it is suitable for use in just about any environment. Given its power, the Optomux ASCII protocol is extremely simple to use. Almost every third-party MMI or control package has a driver to support the Optomux protocol.

Q: What are the limitations of the Optomux system?

A: The primary performance limitation of the Optomux system is the serial data link. While this link is very secure, and completely error-checked, it is not as fast as a parallel link like Opto 22’s Pamux system uses. The maximum baud rate supported by the Optomux brain boards is 38.4 Kbaud; the maximum usable baud rate for a given system is also typically dependent on the length of the communication lines. In theory, at maximum speed, the Optomux system should be capable of polling roughly 3,400 digital positions per second, or roughly 600 analog positions per second. That’s assuming that all the positions are on the same brain board, which is not possible with Optomux. A more realistic speed figure would be about half of the previous numbers. For faster serial data communication, Opto 22’s Mistic protocol and hardware may be used at speeds to 115.2 Kbps. Or, a B3000 brain using the Optomux protocol can communicate at similar high speeds.

Q: What comprises an Optomux system?

A: An Optomux system is typically made up of three main elements:
  • First, there must be a host device to poll the Optomux brain boards.
  • Second, there are the brain boards themselves, anywhere from one to 255 of them.
  • Last, each Optomux brain board attaches to an I/O mounting rack, carrying the individual I/O modules.
Q: Does Opto 22 have software support for Optomux equipment?

A: Opto 22 has a series of drivers for Optomux, intended for use under DOS, Win16, and Win32 operating systems. In addition, Opto 22 has a generic Optomux driver that may be used with almost any C compiler on just about any processor platform, though this driver does not have built-in serial communications handling. These drivers are contained in the OptoDriver Toolkit. Opto 22 does not have an MMI or control package for use with the Optomux family. The Optomux ASCII serial protocol has become an industry standard, however, and many MMI and control interface software packages are available with Optomux drivers.

Q: Can I use Optomux on a 2-wire RS-485 serial link?

A: In theory, it should be possible, but Opto 22 does not recommend or support Optomux used in 2-wire mode. This means that if you figure out how to do it, great, but we won’t be able to help if you have a problem. If you want to use 2-wire RS-485 communications, Opto 22’s Mistic protocol and equipment is designed around such a communications bus.

Q: Is it possible to put other serial devices on the Optomux network?

A: Yes, this is possible as long as the devices are tolerant to the Optomux protocol, and as long as the serial device’s communications protocol can be ignored by the Optomux brain boards. All valid Optomux host messages begin with ASCII character 62 (>); all other messages on the link will be ignored. As long as character 62 is not used by the additional serial device, everything works. Opto 22 also makes an addressable interface converter called the AC31. This device lets messages be sent to RS-232 devices connected to the RS-422/485 network. More than one AC31 can be installed on the network, since they are addressable like Optomux brain boards. Essentially, the host sends an ASCII message to the AC31, framed by an Optomux style packet. The AC31 strips off the header and checksum elements of the packet, and passes the rest of the message to the RS-232 device.

Q: Does Opto 22 make a power supply for Optomux equipment?

A: Opto 22 manufactures a series of power supplies usable with digital Optomux equipment. They are the PBSA (120 VAC), PBSB (240 VAC), and PBSC (12/24 VDC). The power supplies attach to contact points on Opto 22-H suffix digital I/O module racks, and will sit under a brain board if one is installed. Opto 22 does not have a power supply for analog I/O systems. In any event, a well-regulated, linear supply should be chosen, with careful attention paid to be certain the supply can supply the needs of the brain boards and the modules. Please request Opto 22 application note TN9602 for more information.

Q: Will old Optomux equipment work with new Optomux equipment?

A: Yes; current Optomux hardware will work in conjunction with old Optomux equipment with no problem at all. One word of caution, however; over the years, new commands have been added to the Optomux protocol. New boards still support the old commands, but old boards may not support the new commands. Thus, new Optomux driver software may not necessarily function with old Optomux brain boards.

Q: Is analog Optomux available with more than 12-bit resolution?

A: At one time, there existed a 14-bit version of analog Optomux. Opto 22 does not offer this anymore, due to some technical problems with the design. Currently, all Optomux is 12-bit resolution, plus half-resolution over-range.

Q: Can I use my Optomux system with the newer Mistic equipment?

A: Yes, though the two protocols will not coexist on the same serial data link. Mistic brain boards use a binary protocol on a 2-wire RS-485 link as a default; Optomux will not function in this mode. Opto 22 does have a set of subroutines available for the Mistic 200 controllers, allowing them to communicate with Optomux brain boards through the Mistic controller’s built-in serial ports.