How To Receive Data On The Usb Connection - Magtek DynaPro Go Programmer's Manual

3 - Connection Types

3.1.4 How to Receive Data On the USB Connection

When the device communicates with the host as a vendor-defined HID device, it sends unsolicited
messages to the host via one or more Input Reports, which are asynchronous data packets (i.e., events)
sent from the device to the host using the USB Interrupt IN pipe. Events occur when the device state
changes or when an asynchronous command (such as a command that requires cardholder interaction) has
completed.
Per the USB HID standard, the host polls the device on a regular Polling Interval to see if it has input data
available to send. If the device does not, it responds to the poll with a USB NAK. The host software
should listen for input reports, and upon receiving one, process it as follows:
1) Determine the incoming input report's Report ID.
2) Look up the corresponding Report ID in this document (for example, Report 0x20 - Device State
Report uses Report ID 0x20).
3) Parse the data in the input report according to the report's documentation. Optionally the host may
examine the Usage for that report, and interpret the incoming data according to that.
4) Respond accordingly (for example, by sending followup commands).
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