View Full Version : Loopback No, Echo Yes with a USB to Serial Adapter on Vista

09-14-2008, 02:12 AM
I bought a Prolific USB-to-Serial Bridge on eBay and got it installed on a Vista Laptop, however, when I run Identity from the Basic Stamp Editor all I get is Loopback No, Echo Yes. What is loopback and why would it fail?

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Mike Green
09-14-2008, 02:22 AM
If you look at the schematic in the Basic Stamp Reference Manual for connecting a Stamp for programming, you'll see that there's a jumper between DSR and RTS. Loopback tests that the jumper is in place. Many USB to serial adapters don't properly implement handshake signals like DSR, RTS, DTR, and CTS. The Stamp itself requires DTR and the Stamp Editor requires DSR and RTS. Your Prolific adapter/bridge probably doesn't implement it.

Keyspan's High Speed USB to Serial Adapter works fine for programming Parallax devices and adapters that use the FTDI chip also work fine.