Brain Products Press Release October 2011, Volume 40 Support Tip Did you know how to set up the digital port settings for a BrainAmp? by Katja Wust and Dr. Davide Riccobon The amplifier‘s PCI adapter card or USB2 Adapter incorporates a 26-pin HD sub-D socket for recording synchronous events such as stimuli or test subject responses. The socket contains 16 1-bit digital inputs that can be individually programmed via the Recorder software. Figure 1: PCI adapter card and USB2 Adapter For each group of 8 bits (bits 0 through 7 and bits 8 through 15) you can define whether the trigger signals are interpreted as highactive (5 V = active) or low-active (0 V = active). In the first case, a marker is written when the trigger signal goes from 0V to 5V (rising edge). When the option low-active is selected, a marker is written when the trigger signal goes from 5V to 0V (falling edge). You can also record the length or duration of the trigger by checking the “Both Active” box for the desired bit or bits. The positive and negative edges are both taken into account, and two markers are written. These markers indicate the start and end of the stimulus or response duration. For example, the marker “S 1_on” is written at the moment the stimulus begins, and the marker “S 1_off” is written at the moment the stimulus ends. Similarly, the duration of a test subject response can be recorded using the markers “R 1_on” and “R 1_off”. Note that this function is not available for the „DC Correction“ marker type. In the “Enabled” column of the table, you can specify whether or not the associated bit is to be evaluated. In the “Type” column, you can specify what marker type each bit represents. It is also possible to assign the same type to several different bits. In principle, the name of the type can be selected freely. However, you should note that the Recorder and Analyzer software use color coding for the visual representation of certain marker types. A red bar represents a marker of the type Stimulus, a blue bar represents the type Response and a yellow bar the type DC Correction. Any other type is represented in Recorder by means of a black bar. For this reason, it is advisable to choose ”Stimulus“ and ”Response“ for the stimulus and response inputs respectively. This way you can distinguish the two marker types on a visual basis also. www.brainproducts.com The ”DC Correction“ marker type is also available if you are carrying out a DC measurement. You can define this for any bit position that you select from 0 through 15. DC offset correction is automatically performed when this marker is received. If several markers of the type ”DC Correction“ are set simultaneously, correction is only performed once. This applies both to USB and PCI ports. The description of the markers is encoded Figure 2: Digital Port Settings automatically in accordance Dialogue with the following procedure: The first occurrence of the type in the table is assigned a value of 1, the second occurrence is assigned a value of 2, the third a value of 4, etc. For every data point, all set bits of a given type are added together in accordance with this pattern. Combining the resulting number with the initial letter of the type generates the description Example Bit 8 through bit 15 are of the type ”Response“. If bits 11 and 13 are set, this results in a marker of the type ”Response“ with the description ”R 40“. Bit 11 has a value of 8 and bit 13 a value of 32. The total is 40. The consequence of this logic is that only markers of different types can be detected at any one time. If you want to record different responses simultaneously, you can do so subsequently by decoding the number values in the analysis, i.e. by assigning a separate marker to every bit. Alternatively, you can assign a separate type to every bit in the table. You can view the current state of the digital port for test purposes in the Current State field. Another option available in the Digital Port Settings dialog box is debouncing. If you check the ”Enable Debouncing in Millisecond (5-50 ms)” box, repeated markers of the same type and description are ignored for a period of 5 through 50 ms. Note that the trigger signals must be present for at least the duration of a sampling point. This means, for instance, that at a sampling rate of 1000 Hz, the minimum length of the trigger signal needs to be 1 ms. At 500 Hz, the minimum length needs to be 2 ms, etc.. page 14 of 18