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The Microcoin QL uses pin 6 for an inhibit function. Their tech note says ground the pin, still no joy. 

TL;DR

The company’s tech note describes pin 6, V_inhibit.  See below. By default, the pin is floating, the default way most of us would connect the acceptor and get it enabled. But no luck. So I tried Ground, still no joy. I even tried positive voltage, but certainly did not believe at this point. Here's the excerpt for pin 6:

Spoiler alert: There’s more to the story and use of pin 6. The acceptor activates when pin 6 is grounded and the acceptor is constantly polled. And for that to happen, the adventure transitions to ccTalk and commands sent over its data line.