USB-to-serial adapter sink current?

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1

Any idea how much current the CP2102 chip’s digital lines can safely sink? The datasheet doesn’t seem to say, or at least I didn’t find where it does.

I would like to use the RTS pin on a USB-to-serial adapter to simultaneously reset two SMC03s. Since they’ll be running continuously (well, for about one minute every half hour, but I do mean every half hour) I want to reset them before sending new commands just in case. The problem is that even in the high state the RTS pin is only at 3.3V. If I connect the pins directly, most of the time it would be sinking 3.4 mA, and 10 mA briefly during reset. I suppose I could halve that if I connect one SMC03 to RTS and one to DTR.

If I can’t find real specs though I think I’ll just build in a double transistor inverter.

-Adam

2

Adam,

I think the 10 mA should be safe, but I don’t know what you mean by the double transistor inverter. Why not just use a single transistor in an transistor-resistor inverter? You already have the pull-up resistor, so you just need the transistor (and a base resistor).

- Jan

3

I have a single transistor inverter set up now, but since RTS is normally high I would like that to be the operating state of the board, and reset them by pulling it low. That way I can plug it into any computer and have it operate normally without having to manipulate the handshaking lines.

I just realized I have a bunch of 78LS04’s (hex-inverters) in my desk anyway though, so double-inverting is going to be a breeze!

-Adam