Hi Mike,
> What's wrong with the simple Open Collector level shift idea? You have
> access to the 3.3 supply on the DIO as I recall.. just wondering what
> you're thinking is there.
I looked back at your suggestion:
> Try using any 5V open collector gate with it's output pulled up
> to 3.3V. You don't need any fancy bus transceiver to do what
> you're doing.
This requires two supplies, and those two supplies should
really come from the same source, eg. the SBC.
The requirements were to both transmit and receive:
> I need both to drive 5V TTL devices as well as get input
> from 5V TTL devices
The receive version needs to be careful about power-sequencing,
since you don't want the external device parasitically powering
the SBC when its shut-down.
Its quite possible you can use an open-collector driver to do
this.
For example, see the circuit I mentioned in the previous email.
I use a TinyLogic tri-state driver powered from 3.3V, with inputs
at 3.3V levels, and with an output pull-up to 5.5V. The output
logic levels are ternary; 0V, 3.3V (tri-state enabled) and
5.5V (tri-state disabled and pull-up active). The ternary
logic is needed by the hot-swap controller I2C addressing
interface.
Cheers,
Dave
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