blocking ttl serial transmit

max72

I have a chip sending I2C and serial data.
Both are 5V levels.
For safety reasons I should be able to block the data transfer in case of need.
I found some I2C repeater chips with enable pin that are just perfect for my I2C bus.
I'm wondering if there is a similar solution for the serial bus.
Thanks in advance,
Massimo

JonnyMac

If your serial device drives its TX pin high you can insert a 3.3K resistor between it and the Propeller. If it uses an open-collector/drain configuration, a pull-up (like on I2C) is the only requirement.

If you really want something more between the Propeller and your device, the attached circuit works well for serial and I2C signals. I use this interface for communicating with Dynamixel actuators.

max72

Thanks Jon,
but I have no control on both ends of the bus.
I can only insert a chip controlled buffer that I can switch off in case of need. For the rest of the time the system should work as usual.
The prop would receive the shutdown command, and via an optocoupler (separate supply) cut the transmission.
The I2C switch would be something like texas TCA4311
I'm looking for a similar neat solution for the serial bus.
Massimo

Sapphire

What about an AND gate? One input is your control, the other is the TTL serial. If control is low, output is low. If control is high, then the output follows the TTL serial input.

max72

Thanks,
An AND gate is a very nice option.

Have do get a couple of chips and test them..
Thanks.
Massimo

kwinn

AND a single quad AND gate chip can control a single I2C and two serial signals, two I2C signals, or four serial signals.