C51: Declaring External sbit Variables

Information in this article applies to:

• C51

SYMPTOMS

I have declared an sbit called foo in a source file called bar.c:

bdata char dummy ;
sbit foo = dummy ^ 3 ;

In another source file, I have tried to declare the sbit as extern:

extern sbit foo;

However, when compiling I get a syntax error. What am I doing wrong?

RESOLUTION

When declaring an sbit as extern, you must use the 'bit' type. For example:

extern bit foo;

Note: this only works for sbit variables in the bit-addressable memory range 0x20 - 0x3F and not for SFRs declared with sbit.

MORE INFORMATION

• Refer to sbit in the Cx51 User's Guide.
• Refer to bit in the Cx51 User's Guide.
• Refer to Bit-Addressable Objects in the Cx51 User's Guide.

Last Reviewed: Thursday, February 25, 2021