Hold it in idle

What would be the best way to get UART TX line to stay low after a package (number of bytes) have been sent?

I need to hold it low for 10 bits (104us) after all bytes are sent.

Isn’t this called a “break condition”?

I’m not sure if serial breaks are supported in NETMF, but depending on your processor, you may be able to use the Register class to send a break. For example, the LPC1788 used in the G120 apparently has an LCR register which allows you to send a break if Bit 6 is set High. I haven’t tested this though.