Help needed in dereferencing a union

Working on an embedded controller, I generally find it convenient to
define the following de-referenced pointer:

#define portb (*(unsigned char *)(0x03u))

This enable me to write to a port as follows:

portb = 0x0f;

But when I want to define a register as follows, the code does not
compile:

typedef union
{
uint8 byte;

struct
{
uint8 : 4;
uint8 tffca : 1;
uint8 tsfrz : 1;
uint8 tswai : 1;
uint8 ten : 1; /* timer enable */
}bit;

}tSCR1;

#define scr1 (*(tSCR1 *)(0x4c))

useage:

scr1.bit.ten = 1; /* the compiler complains about this */

I find it very convenient to use this scheme if possible. It is very
clear what is being manipulated just by reading the code. I prefer
this over: "scr1 = 0x01;". Is it possible to dereference this union
in the same fashion as the first example? Thanks very much in advance.

.