MCP23S09 VS MCP23S17 IO expander

Ian0

Joined Aug 7, 2020
9,519
No, you can decide which one you are addressing by using the CS line. (Though if you had a spare IO line to connect to CS, why would you need an IO expander?)
 

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Alex1700

Joined Jan 12, 2020
107
No, you can decide which one you are addressing by using the CS line. (Though if you had a spare IO line to connect to CS, why would you need an IO expander?)
thanks, I forget about CS then may I know what is the use of the address pin in MCP23S17 the reason I need to use the IO expander as I need to control the 100++ relay switch on and off
 

Ian0

Joined Aug 7, 2020
9,519
You can also use a 74HC138 to generate eight CS signals from 3 outputs (or a 74HC154 to generate 16 from 4), but watch the maximum fan-out from the MCU. You might need to buffer MISO and SCK.
Alternatively, Microchip make some expanders with I2C interfaces.
 
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