Use this to update the Garmin 18x pc gps receivers to firmware 
version 4.20. This this version has a fix for the April 6th 2019
rollover issue. 


-Load Garmin Installation instructions if you prefer to follow that.
 otherwise continue below.
 
 https://www8.garmin.com/support/download_details.jsp?id=4055#Instruct

-Download 4.20 update and extract the binary to C:\Garmin.
 http://download.garmin.com/software/GPS18xPC_LVC_420.exe
 
-Extract "GPS18xPC_LVC_420.exe" by running it. 

-Start the SNSRXCFG_200 program and select GPS 18x PC.

-From the "Comm" menu select the appropriate serial port,
 and set a manual baud rate of 4800.
 
-From the "Comm" menu select "connect".

-From the config menu select "Update Software".

-Select the following file "079601000420.rgn"

-When asked for update program, slect the "Updater.exe" program that was
 just extracted. At this point SNSRXCFG_200 should start Updater.ex
 if it doesn't, close SNSRXCFG_200 and run Updater.exe
 We had to do this with Windows 10.
 
-Now select correct serial port and set a baudrate of "115200"
 This might take a while.
 
-Remove and reconnect the power to the unit in order to reboot it.

-Open a terminal program like Hyperterminal, putty, minicom ect..
 to make sure NMEA sentences are steaming.
 Set the conection to 4800,8,N,1