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[RogerN]

I'm working on an I/O board that goes from serial up to 24 Opto22 compatible
I/O modules. So far it is configurable to have any point be an input or
output. The problem is that if the user needs 24 outputs, and all on at the
same time, the microcontroller can't drive that many 12mA outputs.

I need something that can output 5V at approximately 20mA but can be used as
an input if the microcontroller pin is configured for input. Maybe
bi-directional self switching transceiver?

Thanks!

RogerN

 

[Tilmann Reh]

RogerN schrieb:

I'm working on an I/O board that goes from serial up to 24 Opto22 compatible
I/O modules. So far it is configurable to have any point be an input or
output. The problem is that if the user needs 24 outputs, and all on at the
same time, the microcontroller can't drive that many 12mA outputs.

I need something that can output 5V at approximately 20mA but can be used as
an input if the microcontroller pin is configured for input. Maybe
bi-directional self switching transceiver?

What about a BJT as emitter follower, with an additional resistor
between B and E that feeds the signal back to the port in input mode?

Tilmann

 

[Andrew]

RogerN wrote:

I'm working on an I/O board that goes from serial up to 24 Opto22 compatible
I/O modules. So far it is configurable to have any point be an input or
output. The problem is that if the user needs 24 outputs, and all on at the
same time, the microcontroller can't drive that many 12mA outputs.

I need something that can output 5V at approximately 20mA but can be used as
an input if the microcontroller pin is configured for input. Maybe
bi-directional self switching transceiver?

Thanks!

RogerN

74HCT245?

http://www.fairchildsemi.com/ds/MM%2FMM74HCT245.pdf