More than 4 MCP23S17 on 1 SPI bus
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