i2c io expanders
Posted: Tue Feb 14, 2023 4:57 pm
PCF8574 from nxp is well known enough
https://www.nxp.com/docs/en/data-sheet/ ... F8574A.pdf
But i don't really like the 'quasi bidirectional io'
nevertheless, these seemed to be the most prolific
https://www.aliexpress.com/af/pcf8574.html
then as i dug further around
I stumbled into tca9534a from TI
https://www.ti.com/lit/gpn/tca9534a
then pca9535
https://www.nxp.com/docs/en/data-sheet/ ... 535CDS.pdf
https://www.ti.com/lit/ds/scps129k/scps129k.pdf
and pca9555
https://www.nxp.com/docs/en/data-sheet/PCA9555.pdf
https://www.ti.com/lit/gpn/pca9555
they looked nearly identical except that in pca9555 it has an internal pull up resistor to VDD
fig 7, fig 8
pca9535, pca9555 seemed to be priced similarly
https://www.aliexpress.com/af/pca9535.html
https://www.aliexpress.com/af/pca9555.html
and it seemed they are 'less popular' compared to the 'old' PCF8574 as modules for these seemed 'absent' from AliX
for practical purpose, these are only useful as 'extra hands' to provide single bit gpios at each pin, it is unlikely to handle any faster switching speeds partly limited by i2c 400kbps.
they are rather useful as 'single chip' keyboard scanners vs using 74hcxxxx (e.g. 74hc595 and 74hc164 shift registers)
but are costier
i'd guess it is simplier to use a bigger stm32 chip with more pins than do use 'i2c io extenders'
but for 'low pin count' chips e.g. so8 or so20, i'd guess they may at times comes handy
https://www.nxp.com/docs/en/data-sheet/ ... F8574A.pdf
But i don't really like the 'quasi bidirectional io'
nevertheless, these seemed to be the most prolific
https://www.aliexpress.com/af/pcf8574.html
then as i dug further around
I stumbled into tca9534a from TI
https://www.ti.com/lit/gpn/tca9534a
then pca9535
https://www.nxp.com/docs/en/data-sheet/ ... 535CDS.pdf
https://www.ti.com/lit/ds/scps129k/scps129k.pdf
and pca9555
https://www.nxp.com/docs/en/data-sheet/PCA9555.pdf
https://www.ti.com/lit/gpn/pca9555
they looked nearly identical except that in pca9555 it has an internal pull up resistor to VDD
fig 7, fig 8
pca9535, pca9555 seemed to be priced similarly
https://www.aliexpress.com/af/pca9535.html
https://www.aliexpress.com/af/pca9555.html
and it seemed they are 'less popular' compared to the 'old' PCF8574 as modules for these seemed 'absent' from AliX
for practical purpose, these are only useful as 'extra hands' to provide single bit gpios at each pin, it is unlikely to handle any faster switching speeds partly limited by i2c 400kbps.
they are rather useful as 'single chip' keyboard scanners vs using 74hcxxxx (e.g. 74hc595 and 74hc164 shift registers)
but are costier
i'd guess it is simplier to use a bigger stm32 chip with more pins than do use 'i2c io extenders'
but for 'low pin count' chips e.g. so8 or so20, i'd guess they may at times comes handy