Using the TEC Controller's Passthrough Feature

Table of contents

1. Introduction

2. Physical setup

3. How it works

4. Enabling passthrough

5. Fault handling

6. Autostart

7. WinVue support

1. Introduction

The Vue-TEC is capable of forwarding serial commands to a second controller connected to its “RS-232 out” connector. If this second controller is a VueMetrix product, the Vue-TEC can synchronize certain operations between the two units. The combination of two controllers appears to the user as if it were a single device, with one serial connection to the host PC and the possibility of stand-alone operation using the “Autostart” feature. This manual supplement explains this in detail.

2. Physical setup

The physical arrangement of the two controllers is depicted in the figure. The second or “downstream” controller is connected to the TEC controller's “RS-232 out.” The host PC is connected to either the TEC controller's “RS-232 in” or its USB port. If the TEC controller's Autostart feature is enabled the PC connection is not necessary.

3. How it works

Commands to the TEC controller with a leading '!' are relayed to the downstream controller. These commands must be terminated by a '#' character. All of the characters between the leading '!' and the trailing '#' are transmitted verbatim to the downstream controller. Any delimiters required by the command syntax of the downstream controller must be included. The communication between the TEC controller and the downstream controller is fixed at 115200 baud, 8 data bits, 1 stop bit, no parity.

After a passthrough command has been transmitted to the downstream controller, the TEC controller will monitor its RS-232 out port for a reply. Replies are assumed to be terminated by a carriage return/line feed combination. When a valid reply has been received, the TEC controller transmits it verbatim (including the terminating <CR><LF>) to the host. During this process the standard VueMetrix handshaking protocol is in effect: the controller will not respond to additional input characters from the PC host until it has sent an answer to the previous command. After the answer is sent the TEC controller resumes listening for new commands. If the downstream controller has not responded after 800 milliseconds, the TEC controller sends an error message “passthrough timeout” to the host and resumes listening.

This protocol works with any VueMetrix controller as the downstream device. As some other instruments may not work with this protocol, contact us if a custom solution is required.


With a Vue-MV as the downstream controller, send the command “!sn?>#' to the TEC controller. The reply will be something like “1234<CR><LF>”, the serial number of the MV controller. It is as though the command set of the TEC controller has been extended by the MV command set, with the MV commands wrapped between '!' and '#'.

4. Enabling the passthrough feature

Passthrough is always available and does not require a special command to activate it.

5. Fault handling

The TEC controller is capable of notifying the downstream controller in the event of a fault. This feature is activated by sending the serial command “ptf 1” and deactivated by sending “ptf 0”. Since this setting is stored in non-volatile memory it remains in effect after a power cycle. When this feature is activated and a fault occurs in the TEC controller, it will send the command “l0” (laser off) to the downstream controller. This allows the combination of two controllers to operate just like the standard VueMetrix DPSS or HCT products: a fault in the temperature servo will shut off the laser, but a fault in the laser drive will not disable the temperature servo.

When passthrough fault handling is active (ptf 1) and the “cf” (clear fault) command is sent to the TEC controller, it will clear its own fault condition and automatically forward a “cf” command to the downstream controller.

Note that on WinVue versions configured for passthrough operation, the “ptf 1” command is issued automatically every time the program is launched.

6. Autostart operation

For autostart operation the combination of two controllers is designed to work together. The TEC controller is the “master” and will not initiate the downstream controller's startup sequence until the temperature is in regulation. In order to configure the controllers proceed as follows:

  1. Send the command “ptf 1” to the TEC controller (WinVue does this automatically).

  2. On the TEC controller, set the desired temperature.

  3. On the downstream controller, program the relevant Autostart operating parameters – operating current or laser power, pulsed or CW, etc.

  4. On the downstream controller, do not enable Autostart on power up. The TEC controller will send a command to the downstream controller at the proper time.

  5. On the TEC controller, enable Autostart.

  6. Turn both controllers off and back on together.

On power-up the TEC controller adjusts the temperature while the laser controller waits. When the temperature is stable the TEC controller sends a command to the laser controller to begin its power-on sequence. This will occur automatically without any intervention from an external computer.

7. WinVue support

Versions of WinVue are available that support the passthrough feature, allowing a single WinVue program to communicate seamlessly with both controllers. These programs are essentially a combination of the two single-controller versions, with some of the windows communicating with the TEC controller and some communicating with the downstream controller. In the “View” pull-down menu, the passthrough windows are identified by the word “passthrough” in their title, and this word also appears in the title bar for each window when it is opened. The Main Laser control window displays the serial number of the downstream controller. The Main TEC window displays the serial number of the TEC controller.

In some cases there will be two distinct copies of the same window, for example the Service and Utility windows. Note that in the Utility window for the downstream controller, the “Type a command” feature does not require the passthrough syntax. For example, typing sn? and hitting Enter will correctly retrieve the serial number of the downstream controller.

WinVue will display any fault that occurs in the TEC controller or downstream controller. When the Clear Fault button is pressed, faults will be cleared in both controllers.

For documentation relating to these versions of WinVue, refer to the individual manuals for the TEC and the downstream controller.


Do not attempt to use a version of WinVue designed for passthrough operation when no downstream controller is connected, or when the downstream controller is turned off. Always use the standard TEC-only version of WinVue under these conditions.