## Physical Device Driver Reference

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### PRT_QUERYDEVICEID (74h) - Remarks

Before issuing the Query Parallel Port Device ID IOCtl, a valid reverse channel communication mode must be requested using the Set Parallel Port Communication Mode IOCtl. The parallel port device driver uses the communication mode specified by the Set Parallel Port Communication Mode IOCtl when requesting the Device ID string from the peripheral.

Only IEEE-1284 compliant devices return the Device ID. The parallel port device driver returns as much of the Device ID string as there is buffer available to receive the Device ID string. The parallel port device driver uses the length of the data packet specified on the 16-bit DosDevIOCtl2 or the 32-bit DosDevIOCtl call to determine the size of the buffer.