What is default state of PXI 8433 TXD outputs?

[qman]

I have two functional testers which contain NI PXI 8433/4 RS485 cards.   Was swapping between two PCs to control one tester.  Had an application where I use the RS485 instrument in half-duplex configuration to send a couple of bytes to a UUT and the UUT responds back with a byte.  Using one PC, the transfer worked as expected.  Using the other PC, the RS485 instrument appears to be driving all of the time and degrading the signals on the RS485 when the UUT attempts to talk.  (Signals were observed with an oscilloscope).   I now have a reproducible case with one PC;   1)  Scope is connected to TXD+ and TXD- with PC off, but PXI chassis is powered on, 151 ohms between TXD- and TXD+.   TXD- and TXD+ have no diff voltage as observed with scope.   Boot PC normally and soon after the "Windows" logo with the progress bar appears, the scope shows a differential voltage of about 3 volts across the 151 ohm load.  Remove the load and the diff voltage goes to 5V.  This persists and even when I run my application which specifically sets the mode to 2 Wire Auto, the voltage is still present.   It appears that the RS485 driver is always on.   When I shut down the PC (not the PXI chassis), the diff voltage goes away.  If I boot the same PC in safe mode, the diff voltage never appears.   Of course, I cannot run my application because the serial device driver is not loaded.   So, it appears that just loading the serial device driver, causes the driver to turn on.  There appear to be two drivers involved, niserial.sys and mf.sys.    If I boot in Normal mode so that the voltage is present after boot up and then disable the mf.sys driver using Device Manager on the Multifunction Devices, the voltage disappears.   I would like to understand the default state of the PXI 8433 card.   I looked at the physical card, followed the traces, and saw that there is a MAX8036 device which drives the TXD-/+ pins.   Is the circuit designed such that this device is guaranteed to be "off" whenever the PCI of the PC is inactive?  I would also like to understand what simply starting the mf.sys and niserial.sys drivers does to the PXI 8433 card.   This same behavior has been observed on two completely independent testers that is, different PCs, different PXI chassis, different PXI 8433 cards.  Attached scope snapshots, one showing TXD+/- with PC off, PXI chassis on the other after PC boots normally.

[qman]

Figured it out by myself. The default state of the RS485 transmitter is set in the Windows Registry.  See the following;  (TranscieverMode determines the default mode of the RS485 transmitter)   Someone apparently had monkeyed with the Registry on one of my PCs...

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Enum\MF\PCI#VEN_1093&DEV_70ED&SUBSYS_70ED1093&REV_00\a&14910dbd&0&786068686848F0#Child0003\Device Parameters]
"PortName"="COM11"
"PollingPeriod"=dword:00000000
"NIPortNumber"="Port1"
"DceSupported"=dword:00000000
"ForceFifoEnable"=dword:00000001
"BiasEnabled"=dword:ffffffff
"BiasLevel"=dword:ffffffff
"SerialNumber"=dword:0122f0e6
"IoManagementScheme"="DMA"
"InterruptManagementScheme"="Mailbox"
"ResourceWindowType"="Memory"
"ResourceWindowOccurrence"=dword:00000000
"IoBridgeType"="MiniMite"
"SerialControllerType"="Oxford16c954"
"FifoRxMin"=dword:00000001
"FifoRxMax"=dword:0000007f
"FifoRxDefault"=dword:00000040
"RxFIFO"=dword:00000040
"FifoTxMin"=dword:00000001
"FifoTxMax"=dword:00000080
"FifoTxDefault"=dword:00000080
"TxFIFO"=dword:00000080
"ClockFrequency"=dword:03840000
"BusType"="PXI"
"Series"="8433"
"Standard"="RS-485"
"TransceiverMode"=dword:00000083
"MaxBaudRate"=dword:002dc6c0
"Isolation"="1"
"NumberOfPorts"=dword:00000004
"MAX_Name"="PXI-8433/4"
"ResourceWindowOffset"=dword:00000800