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Stimulus Delivery & Triggering

Info

The Stim PC (CHBH-ST-MEG-W02) has no on-board parallel port.
It is utilising a PCIe(x1) parallel port card by Delock, with the Oxford Chipset.
This particular card (#89219) been shown to work well with Presentation, PsychoPy, Psychtoolbox (MATLAB)

To install, and use, a Delock 89219 PCIe Parallel Port card, see Delock Parallel Port Card

Parallel Port Connections to MEG hardware

The CHBH-ST-MEG-W02 parallel port is connected to the MEG acquisition electronics via the 37-pin multipole connector of Stimulus Trigger Interface #1 (STI101). No BNC triggers are made from the parallel port.
The 8 data lines of the parallel port are connected to Trigger Inputs 1-8 ("In 1", "In 2" etc.) of the STI101. Trigger line logic in the MEG is explained below.

The Stimulus Trigger Interface BNC connectors and the 37-pin multipole connector are internally connected together.
DO NOT connector the multipole connector if individual triggers via the BNC connectors are to be used.

CHBH-ST-MEG-W02 Port memory base address: 0xCFF8 (LPT1)

Within MATLAB (Psychtoolbox), 64bit

(This has already been done for CHBH-ST-MEG-W02)

A C++ extension (mex file), created by Prof. Frank Schieber (Department of Psychology, The University of South Dakota), is used to accomplish very fast port I/O, as a NO COST add-on to MATLAB, using native methods to access low-level hardware.

Prof. Schieber has since retired, and his website is down, but web.archive.org has a snapshot of it ...

Mex-File Utility for Fast MATLAB Port I/O (64-bit)

This mex-file is named io64.mexw64. It uses a freeware self-installing system driver named inpoutx64.dll

Note

Self-installation of the driver requires that the MATLAB runs with Administrator privileges. The driver must have been previously installed in order to support non-Administrator users].

  • Download the io64.mexw64 module and place it in the relevant stimulus delivery folder (or as necessary in the MATLAB path).
    If not done, then on useage the following error will be generated ...
>> Undefined function or variable 'io64'
  • Download the inpoutx64.dll module and move it to the C:\Windows\System32 directory (i.e., This module must reside in the Windows system PATH).

Note

Because the inpoutx64.dll was compiled using Visual Studio, the Microsoft Visual C++ 2005 SP1 Redistributable (x64) Package must be installed on the computer.
Use the Control Panel to see if it is already installed.
Open Add and Remove Programs and look for Microsoft Visual C++ Redistributable. The installed versions will be listed there.
If not, then vcredist_x64.exe needs to be downloaded and installed (possibly via Administrator privileges).

  • Add the following line to the beginning of the MATLAB script.
address = hex2dec('CFF8');    %CHBH-ST-MEG-W02 Stim PC LPT1 output port address
  • The following MATLAB command snippet demonstrates how to use the io64() extension:
%create an instance of the io64 object
ioObj = io64;
%
% initialize the interface to the inpoutx64 system driver
status = io64(ioObj);
%
% if status = 0, you are now ready to write and read to a hardware port
% let's try sending the value=1 to the parallel port (LPT1)
% address = hex2dec('378');    %standard LPT1 output port address
address = hex2dec('CFF8');     %CHBH-ST-MEG-W02 Stim PC LPT1 output port address
data_out=1;                    %sample data value
io64(ioObj,address,data_out);  %output command
%
% now, let's read that value back into MATLAB
data_in=io64(ioObj,address);
%
% when finished with the io64 object it can be discarded via
% 'clear all', 'clear mex', 'clear io64' or 'clear functions' command.
clear io64;
  • The following MATLAB command snippet demonstrates how to turn all the CHBH-ST-MEG-W02 Stim PC trigger lines on/off.

initialiseParallelPort.m MUST be in the relevant stimulus delivery folder.

sendTrigger = initialiseParallelPort();

for ii = 0:7
    sendTrigger(power(2, ii));
    WaitSecs(0.2);
end

%% Reset Triggers to 0
sendTrigger(0);

initialiseParallelPort.m

function sendTrigger = initialiseParallelPort()
% sendTrigger = initialiseParallelPort()
%
% Tries to initialise a parallel port using the inpoutx64.dll library.
% Returns the function sendTrigger, which takes a single 8-bit integer
% input and sends it to the parallel port. NB: no input checking is done!
% Make sure you only use values 1-255. Also, the trigger lines are not
% pulled down automatically, you need to do this manually by sending a 0:
%
% sendTrigger(15)  % send trigger 15
% ... do something ... e.g. a Screen('Flip')
% sendTrigger(0)  % pull all lines down
%
% If initialisation fails, returned sendTrigger-function simply prints
% out the input code; useful for developing/testing.

% Revision history:
% - created on 26 Jan 2018, cjb
%
% Copyright 2018 Christopher J. Bailey under the MIT License
%
% Permission is hereby granted, free of charge, to any person obtaining a
% copy of this software and associated documentation files (the
% "Software"), to deal in the Software without restriction, including
% without limitation the rights to use, copy, modify, merge, publish,
% distribute, sublicense, and/or sell copies of the Software, and to
% permit persons to whom the Software is furnished to do so, subject to
% the following conditions:
% 
% The above copyright notice and this permission notice shall be included
% in all copies or substantial portions of the Software.
% 
% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
% OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
% MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
% IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
% CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
% TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
% SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


try
    % ------------------------------------------------------------------------
    % INITIALIZE PARALLEL PORT
    % ------------------------------------------------------------------------
    % Aarhus: based on InpOut-library, and C:\Windows\System\inpoutx64.dll
    % Aarhus: io64.mex in stimuser's Documents\MATLAB-folder (in path)
    % create an instance of the io64 object
    ioObj = io64;
    % initialize the interface to the inpoutx64 system driver
    status = io64(ioObj);
    % LPT1 memory port address
    % address = hex2dec('DFF8');
    address = hex2dec('CFF8');

    sendTrigger = @(code) io64(ioObj, address, code);
catch  % assume either drivers not found or running on non-stim PC
    fprintf(1, '############################################################\n');
    fprintf(1, 'WARNING: No parallel port access, triggers will not be sent!\n');
    fprintf(1, '############################################################\n');
    sendTrigger = @(code) fprintf(1, 'TRIG %d\n', code);
end
end

With many thanks to Dr. Chris Bailey, Aarhus Univeristy

Trigger logic in MEG data

By default, only one trigger channel is sampled with the MEG data: STI101.
This channel contains all possible trigger combinations, up to a theoretical maximum of over 65000 unique triggers.
When all trigger lines are "down" (0), STI101 reads zero. When:

  • A trigger is sent to input 1, height(STI101)= 1
  • A trigger is sent to input 2, height(STI101)= 2

  • A trigger is sent to input 1 AND 2, height(STI101)= 3

  • Following a binary encoding scheme in which input 1 is 20, input 2 is 21, input 3 is 22 and so on.

The following PDF, Triggering_through_the_Parallel_Port, was kindly provided by The Aston Neuroimaging Facility, Aston University.

In summary, the height of STI101 indicates the value of the trigger signal sent via the parallel port, with most values being encoded by multiple simultaneous trigger signals.

If desired, the individual trigger lines (1-16) can also be activated separately, in which case 0 is no trigger and any positive value is a trigger.