Question

I’m trying to understand this embedded c code. I think it means it is connecting port bits to some register in a bus. Correct me if I’m wrong. And what ever changes we make to the ports will be reflected on the bus registers. Here is the snippet of the code. Thanks.

/*--------------------------------------------------------------------------
Local Variables
--------------------------------------------------------------------------*/
// Port bits assigned to Amba Peripheral Bus (APB)
// P0^7..P0^0               // output=reg_addr, input=data_in (APB prdata)
sbit APB_SEL = P1^7;        // select a bus transaction
sbit APB_EN  = P1^6;        // enable/activate a component 0 = disable, 1 = enable

Answer 1

The code is defining bit positions to be read from registers. sbit defines a bit within a special function register (SFR).

sbit APB_SEL = P1^7;

Here P1 is a previously defined SFR. The line defines APB_SEL as bit 7 (zero-based numbering) of P1.

This link has additional details on the syntax.