> On Oct 24, 2016, at 3:55 PM, David Bridgham <d...@froghouse.org> wrote:
>
> On 10/24/2016 12:01 PM, Paul Koning wrote:
>
>> I don't know about the receiver part, but I'd expect that the drivers could
>> very easily be done with a simple transistor circuit.
>
> Agreed. However ...
>
>> As for slew rates, unless you have antique transistors, that's not going to
>> be an issue given that you meet the current sink spec; the slew rate of an
>> OC circuit is determined by the system capacitance and the sink current of
>> the driver.
>
> I think you read this part backwards. The slew rate requirement is not
> a minimum slew rate but a maximum one. That is, any modern transistor
> (probably ancient ones too) will be way too fast. You have to do
> something to slow it down. Still, I think this one is easily met as
> it's just a series resistor on the gate of the driver MOSFET working
> against the gate capacitance. Some FPGAs have current limiting on their
> output which may obviate the need for the resistor even.
I don't see any max slew rate spec in the driver specs in the peripherals
handbook.
paul
