FAQ: Can I send TTL pulses from the EyeLink Host PC to external devices?

[Dan]

While sending TTL pulses for synchronization purposes is typically handled by the Display PC, it's also possible to send TTLs from the EyeLink Host PC. This is a useful option if your Display PC lacks a parallel port, as a message can be sent from the Display PC to the Host PC via the ethernet link, giving a command for the Host PC to send a TTL. This allows key trial events (such as stimulus onset) to be flagged in external recording devices and the Host PC simultaneously.

All desktop EyeLink Host PCs include a parallel port that can be used for TTL input and/or output. Laptop Host PCs for the EyeLink 1000 Plus and EyeLink Portable Duo support TTL output using a USB2TTL8 device. Some laptop models, like the Dell M4700 and M4800, also support ExpressCard parallel port adapters. The specific port address you need to use will depend on your EyeLink system and Host PC, as detailed below.

You can send TTL signals from the Host PC's parallel port by using the write_ioport command within your experimental script. The exact syntax will vary depending on your programming environment.

Code:

## write_ioport <ioport> <data>
;; Writes data to I/O port.  Useful to configure I/O cards.
;;          <ioport>: byte hardware I/O port address
;;          <data>: data to write

The base register for the input will change depending on the device used to receive it. The list below illustrates the commonly used ports for each EyeLink configuration.

• EyeLink II / EyeLink 1000 with a built-in parallel port card:
  
  Code:

  write_ioport 0x378 0xFF
  
  
• EyeLink 1000 Plus destop computer Host PC with a built-in PCI/PCIe parallel port card or laptop with with an ExpressCard parallel port adapter:
  
  Code:

  write_ioport 0x8 0xFF
  
  
• EyeLink 1000 Plus Host (software v5.17 and above) / EyeLink Portable Duo (Host software 6.17 and above) with an external LabHackers USB2TTL8 device plugged into the USB port:
  
  Code:

  write_ioport 0x7 0xFF

If your system has the analog output option, you can also send and receive TTL signals through its four digital I/O registers. (For more details, see Section 7.4, "Digital Inputs and Outputs," in your EyeLink system's user manual.) This is especially useful if the parallel port is already occupied by another device, such as a response pad.