pTAL Reference Manual (G06.24+, H06.09+, J06.03+)

You must specify either referral or structure-layout but not both in an equivalenced
structure declaration.
You can specify a FIELDALIGN clause only if you specify structure-layout. You cannot specify
a FIELDALIGN clause for a referral structure.
Example 129 Declaring Equivalenced Structures
STRUCT a;
BEGIN
INT i;
INT j;
END;
STRUCT b = a;
BEGIN
INT(32) z;
END;
STRUCT c[0:3];
BEGIN
INT i;
INT j;
END;
STRUCT d[0:3] = c;
BEGIN
INT(32) z;
END;
The code in Figure 12 (page 190) declares an extended indirect definition structure equivalent to
a previously declared extended indirect structure.
Figure 12 Equivalenced Definition Structure for CISC Architecture
STRUCT .EXT xstrl;
BEGIN
STRING old_name[0:20];
STRING old_addr[0:50];
END;
STRUCT .EXT xstr2;
BEGIN
STRING new_name[0:30];
STRING new_addr[0:40];
END;
If the new structure is to occupy the same location as the previous variable, their addressing modes
must match. You can declare a direct or indirect structure equivalent to the following previous
variables:
Previous VariableNew Structure
Direct structure Simple variable
190 Equivalenced Variables