More than 4 MCP23S17 on 1 SPI bus

Question

I would like to use 7 MCP23S17 as output expanders on one SPI bus. Every IC has its own address from 0 to 6. The first MCP23S17 can be written with no problem. The second chip did not work properly. The CS pin of the MCP23S17 is set like at the all other 4 ICs.

Does anybody have experience with more then 4 MCP23S17 on SPI? Could anyone help?

#include <SPI.h>
#include <MCP23S17.h>

MCP A(0, 10);
MCP B(1, 8);
int d = 250;

void setup() {
  A.begin();
  B.begin();
  for (int k = 1; k <= 16; k++) {
    A.pinMode(k, OUTPUT);
    B.pinMode(k, OUTPUT);
  }
}

void loop() {
  //////////// ON THE LIGHT ONE BY ONE  FROM BEGGING
  for (int f = 1; f <= 16; f++) {
    A.digitalWrite(f, HIGH);
    delay(d );
  }
  for (int f = 1; f <= 16; f++) {
    B.digitalWrite(f, HIGH);
    delay(d );
  }
  ////////////  OFF THE LIGHT ONE BY ONE  FROM BEGINNIG
  for (int f = 1; f <= 16; f++) {
    A.digitalWrite(f, LOW);
    delay(d);
  }
  for (int f = 1; f <= 16; f++) {
    B.digitalWrite(f, LOW);
    delay(d);
  }
}

Answer 1

 MCP A(0, 9);                              
 MCP B(1, 8);
 MCP C(2, 7);                              
 MCP D(3, 6);
 MCP E(4, 5);                              
 MCP F(5, 3);

• CS on pin 10 is often used for Ethernet
• CS on pin 4 is often used for SD

Answer 2

Assuming that the adressing is correct and all the modules work fine individually, there are some things you can do:

• try to disable the slave select of the modules that aren’t require to communicate at a certain time, there are examples for that

• add a bit of code where you define chip select as an input for all but one and see if you can communicate with that one. Do that for all of them

• remove MISO pin from all but one and see if you can communicate with that one. Do that for all of them

• use a tri-state buffer through which you connect the MISO pin and use chip select for enabling the buffer. This buffer puts the MISO pin into a state of high impedance when a certain module is not used for communication and prevents fata from being lost