Question

C.) An I/O expander MCP23517 along with its connection to PIC are shown below. MCP23917 SDO SI SDI SCK RBO SO ск CS PIC A1 AD A2 Gnd 5v Gnd i. What are read and write OPCODE for this 1/0 expander? (2-marks) ii. Using MIKRO-C Library functions, Write a function namely READ_GPINTENA() in which you have to write necessary 5-6 lines code to read content of GPINTENA reg of slave and save it in a character variable namely STORE Note: No need to write main function or code for TRIS settings of SPI or 1/0 direction setting of slave. Think that it's already done!!! Just write necessary 5-6 lines code in function body to perform given task only. I/O expander Registers address table and OPCODE packet is given on helping sheet. Some Useful MIKROC SPI library functions are : void SPIx_Init(); unsigned short SPIX_Read(unsigned short buffer); void SPix_Write(unsigned short data); (5-marks)

Answer 1

As the Addressing pins of the module are powered as 
A2 = 0 
A1 = 0 
A0 = 1 
So the SPI address of the module is 1 
for Address 1 ,the read and writ Opcodes are
write opcode = 0x42;
read opcode = 0x43;

Code 
function READ_GPINTENA (readopcode){
   Chip_Select = 0 ;
   SPI1_Write(readopcode);      //sending read command
   SP1_Write(0x04);   // sending address of GPINTENA register considering BANK_0 adressing.
   char STORE = SPI1_Read(0xFF);   // sending 0xFF as dummy data data to get response
   Chip_Select = 1 ;
   return STORE;   //returning the store variable 
}