Carry flag value from c code

Don't use internal registers in C! Neither ACC nor B, R0-R7, DPTR and so on.

If you have to use the carry bit CY:
Try to use an equivalent algorithm (see the suggestion from Erik).
If this is not possible or insufficient, then use the alternative solution: It's highly recommended to use CY either as inline assembler (#pragma asm ... #pragma endasm) of a .C51 module/function or in an external .A51 assembler module/function.
And, of course, with own proper initialization of ACC in your asm statements, don't rely on the contents of ACC by the C-compiler!

This suggestion is also valid for checking the parity bit P, which has the same problem as CY.

I often use this technique, e.g. when decoding DCF77 radio clock signal (which has three parity bits).

Martin

Don't use internal registers in C! Neither ACC nor B, R0-R7, DPTR and so on.

If you have to use the carry bit CY:
Try to use an equivalent algorithm (see the suggestion from Erik).
If this is not possible or insufficient, then use the alternative solution: It's highly recommended to use CY either as inline assembler (#pragma asm ... #pragma endasm) of a .C51 module/function or in an external .A51 assembler module/function.
And, of course, with own proper initialization of ACC in your asm statements, don't rely on the contents of ACC by the C-compiler!

This suggestion is also valid for checking the parity bit P, which has the same problem as CY.

I often use this technique, e.g. when decoding DCF77 radio clock signal (which has three parity bits).

Martin

"It's highly recommended to use CY either as inline assembler (#pragma asm ... #pragma endasm) of a .C51 module/function or in an external .A51 assembler module/function."

I highly recommend that you should not use inline assembler - use an external .A51 assembler module/function and call it from 'C'

Inline Assembler is still subject to the risk of false assumptions about the states of internal registers!