The approach won't work. You put the data on the stack in a logical order, but LCALL is going to push the return address onto the stack. So when you arrive at INIT_CARD your stack will contained 149, 0, 0, 0, 0, 64, then the 2-byte return address that will contain the address of the INIT_CARD RET instruction. Then CONTROLCARD is going to push its return address onto the stack each time it calls SENDSPI. So SENDSPI is going to always end up popping one byte of the return address and sending it to the SPI bus. It'll then attempt to RETurn to the calling routine, but the correct return address will no longer be on the stack since you just popped part of the return address and sent it to the SPI bus.

Generally, data is not passed to routines via the stack using an 8052 (though it's not strictly impossible to do so).



The response time is variable. You need to keep reading bytes in from the SPI bus until you find a byte that has its high bit clear. If the bytes you read are 80h or above, you need to keep reading since a return value of 80h or above means the card hasn't responded yet.



No, just pushes the value on the stack. The value in the register you are pushing onto the stack remains unchanged.

Regards,
Craig Steiner