Understanding Digital I/O with TDT

Equipment setups for neuroscience experiments are complex. Even routine behavioral or optogenetic experiments normally involve multiple pieces of hardware and software that need to communicate with one another. Common examples of experiments where devices need to send signals back and forth include: Trigger pulses for external lasers, capture of behavioral events like lever presses, frame synchronization of video cameras, and timing synchronization between two recording platforms. This communication is done using digital input and output (digital I/O) signals on each device.

TDT hardware and software have the ability to communicate with external devices. The most important knowledge for understanding how to setup digital I/O in your experiment is to make sure the hardware connections are correct and that your software is receiving or sending digital I/O on the channel you expect.

TDT Hardware Page

Synapse Digital IO Page

What to Expect

This technical guide will offer readers a full understanding of how digital I/O communication works in TDT equipment and software. This will be done by going over the questions below.

Bit-related:

• What is a TTL pulse? What is bit communication and why do we use it?

• Where and how does TDT receive a TTL pulse?

• How can TDT make and send out a TTL pulse?

• What does this saved data look like?

Byte-related:

• What is a Byte? What is word-communication and why do we use it?

• What is Binary? How do binary numbers related to digital words?

• Where and how does TDT receive bytes?

• How can TDT make and send out a byte?

• What does this saved data look like?

By the end of this guide, you will be able to easily add one or more peripheral devices that sends or receives triggers to or from TDT equipment. If the resources you are needing are not covered in this guide, or if you have any questions that you need help with, please do not hesitate to ask support@tdt.com for assistance.

Common Definitions

Here are some common definitions that you will be exposed to throughout the reading. These also link out to relevant sections:

I/O	Input/ Output
TTL	Transistor-Transistor Logic. This is a fixed high voltage or low voltage signal. Often used in the context of 'TTL pulse'
Bit	The state of a signal that is either voltage high or voltage low
Binary	Something that only has two possible states. In the case of a digital bit, it's 'true' or 'not true'
BNC	A type of coaxial electrical cable commonly used in TTL communication
Epoc	A saved timestamp in your TDT data that marks a digital input or output event
Byte	A set of eight bits that are monitored simultaneously
Digital Word	The numeric decimal value (0 - 255) of a byte
Most-significant digit	The left-most digit in a number representing the largest base group value. The most-significant digit in the base 10 number '137' is the '1' which represents a value of '100 (10 groups of 10)'
Least-significant digit	The right-most digit in a number representing the largest base group value. The most-significant digit in the base 10 number '137' is the '7' which represents how many ones remain in the number when all larger groups have been accounted for
Ground	An important signal line needed for connecting TDT and third-party equipment