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Support    RB-x20 Series Various Protocols Supported by the RB-x20 Series Response Pads

Summary

The RB-x20 generation of response pads is the third one that Cedrus has built and supports three different protocols. This document compares these protocols.

The Available Choices

If you decide to use an RB Series response pad with a program other than the ones described on the RB-x20 Series Support home page, the first task is to chose which protocol suits your application best. A protocol is simply a word for a method or format used to send the information to the host computer.

The three protocols supported are: RB Series, ASCII, and PST SRB. Each has advantages and disadvantages:

Protocol

How it Works

Pros and Cons

RB-x20

Each bit within the byte indicates which key is pressed

One and only one byte is sent every time a key is pressed or released

You can detect when two or more keys are pressed simultaneously

You can detect when a key has been released

It takes some programming to decode the individual bits

ASCII

An ASCII value is sent when a key is pressed

One and only one byte is sent every time a key is pressed

Simplest protocol

You can see readable output from the response device using a terminal emulation program

You cannot detect when two or more keys are pressed simultaneously

You cannot detect when a key has been released

PST SRB (Psychology Software Tools Serial Response Box)

Each bit within the byte indicates which key is pressed

A stream of bytes is sent approximately 800 or 1600 times per second

You can detect when two or more keys are pressed simultaneously

You can detect when a key has been released

It might take some programming to decode the individual bits

The constant stream of bytes makes it more difficult to deal with

Which Protocol to Use

For adapting an RB Series response pad to your own software package, the choice boils down to RB Series or ASCII protocols. We do not recommend the use of PST SRB protocol except with MEL Professional and E-Prime, mainly because the constant stream of bytes can be a hassle to deal with.

If your experiments do not require knowing when two keys are pressed simultaneously or when a key has been released, then ASCII protocol is the simplest and easiest to deal with. Otherwise, we recommend that you use the RB Series protocol.

If you prefer to use the PST SRB protocol, you will need to contact Psychology Software Tools, Inc. directly for information about their Serial Response Box Model 200 protocol.

Last revision:  July 27, 2002

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