>We currently need to create a C# DLL that can be used within VFP to communicate (i.e. send/receive) with an Ingenico 6550 pin pad. I've tried a couple of the different C# open source USBHID libs out there, but we cannot get this to work reliably all the time. Some message sends work and others don't. Some responses come back from the device fine and others don't.
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>Needless to say, Ingenico's test RBA app works flawlessly when communicating with the device, but I don't know what language or API they are using.
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>I was wondering if anyone could please point me to either a working sample app with source, another working C# lib, or some useful information that would help in successfully coding.
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>Thanks.

Wow, their website sucks. I've found most card readers have had either a COM interface I could use or a .NET class I could interface with. I remember looking at the USBHID drivers for .NET at some point and I think I had similar issues - it would randomly lock up or not work. Thankfully I was able to find a more direct driver to use.

Have you tried contacting their support dept. to see what's available? It's obvious they don't make it directly available on their website (or if they do, they've made it nearly impossible to find).