more GPIOs with A20 ( SOM )

[Rajesh Mallah]

We need  a large number of  GPIOs from a given logical system (A20-SOM) to control
large number of other system that depends on logical high or low.

The problem is a single A20-SOM allows upto 64 GPIOs to be exported we need around
100 GPIOs.

How can we extend the original logical system that is running a software to control
more number of GPIOs ?

Regds
Mallah.

[JohnS]

Maybe an I2C I/O expansion chip like PCF8574, e.g. as on small modules on web sites.

John

[soenke]

Depending on the requirements of timing, latency and frequency i see these options:

1) Use a A20-LIME, it has more than 100 GPIOs you could use via /dev/mem very fast and with lowest latency

2) Use an additional A20-SOM or A20-LIME, program a remote procedure call via Ethernet and connect the less timing/latency relevant GPIOs to it

3) Use johns solution via I2C for medium responiveness (1000 times slower than /dev/mem) and a little longer cycle time (1-5ms) in your realtime process.

[Rajesh Mallah]

Thanks Soenke & JohnS,

It does answer my query. I would explore the said possibilities,
and post back what i really chose.


Regds
mallah.

[Rajesh Mallah]

I am also exploring GPIO expander using SPI
http://www.microchip.com/wwwproducts/en/en021817

there seems to be an example (Example2:) worth exploring.
https://www.olimex.com/forum/index.php?topic=232.msg912#msg912