Min usb

The mini USB connector on the GPSmap64 is a data connector and it is possible to configure the 64 to output NMEA sentences over it's USB port, however the uniden home patrol can't receive GPS location data over it's USB port, it can only receive this data over a seperate serial port, this was comptible with the GPSmap60 because this also had a serial port, but as you say the 64 does not have a serial port

The only way you could use the GPSmap64 would be to connect it to a computer that could extract MNEA sentences from the 64's USB connection and then output them via a USB to serial converter into the uniden

 

I think the problem here is that both USB and serial interfaces can be master or slave (controller or controlled), eg. a computer USB port would be a master and a USB card reader would be a slave, on the uniden the serial GPS port is the master and the 60sx is the slave so the uniden controls the transfer of data, however if you connect the uniden serial port to a serial - USB converter and then connect the converter USB to the 64 you are connecting a slave (the converter) to a slave (the 64)

When the uniden was connected to the 60csx there was a serial port (master) talking to a serial port (slave) with the uniden starting the conversation, but if you have the uniden serial port (master) connected to a serial - USB converter (slave) and then to the 64 (slave), the uniden will try to start a conversation but it won't control the serial - USB converter as it doesn't expect it to be there, it would normally be controlled by a computer (master) on the USB side, but in this case the USB side is connected to the 64 which is a slave