OT Hardware Question, Isolating a Shared UART Line

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

I've got a weird situation where I need to use a hardware UART and it is connected to an FTDI USB and a Bluetooth radio. In one situation I need to disable the TX line from the PIC to the Bluetooth radio to prevent the radio from communicating accidentally back to the PIC. I think I've got a signal from the FTDI chip that I can use to "control" the disabling of the TX line but I'm not sure how to do it "gracefully".

Is there a piece of hardware that is meant to achieve this task or maybe some way with discrete components? Even just some terms that would help with a Google search for what I'm trying to do would help.

Thanks,

John

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi John,

I think an 'Analog Switch' would do quite nicely. A number of manufacturers (Maxim, ON Semi) even list 'UART/USB/Data Multiplexing' as a typical application.

John M.

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Perfect!

SN74 Single FET Bus Switch....

Thanks for the help.

asmboy · Joined: 20 Nov 2007 Posts: 2128 Location: albany ny

A pair of 74HC08 and gates - with an inverter driving on alternate gate B select will do nicely as these are only 0-5V or 0-3.3v levels.