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

[Dan]

Often, the sending of TTL pulses can be handled via the Display PC. If the Display PC being used doesn't have a parallel port and / or the Host PC's parallel port is preferred, then it is possible to configure the Host PC to send TTLs to other devices.

• All of the desktop EyeLink Host PCs come with parallel ports installed that you can use for TTL input and / or output. The laptop Host PCs for the EyeLink 1000 Plus and EyeLink Portable Duo support TTL via a USB2TTL8 device.
  
• Some models of the laptop Host PC (e.g., Dell M4700 and M4800) support ExpressCard parallel port adapters as well.
  
• The port address used will depend on which EyeLink system and Host PC is used as described below
  

TTL signals can be sent from the Host PC's parallel port using the write_ioport command (these commands can be sent via the experimental script -- the exact details of the syntax of the commands depends on the 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

;;EyeLink II / EyeLink 1000 with a built-in parallel port card:
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:
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:
write_ioport 0x7 0xFF

If the analog output option is available, TTL signals can be sent and received on the four digital I / O channels (see section 7.4 Digital Inputs and Outputs of the User Manual of the specific EyeLink system).

This can be particularly useful, e.g, if the parallel port is already being used for a response device.