I create a C51 project and write just one A51 subroutine(for speed).I define some SFR in the header file just like sbit FLASH_CS = P1^1; sbit A19 = P3^5; sbit A18 = P3^4; sbit A17 = P3^3; sbit A16 = P3^2; How can I declare them in the A51 subroutine?It seems that the EXTRN directive can't help me!