Atari ST series Technical Reference Manual page 268

Tsetdate()
Sets current date for GEMDOS.
C macro format
int date;
Tsetdate(date);
Machine language format
move.w #date, - (sp)
move.w #$2B, - (sp)
trap #1
addq.l #4,sp
Inputs
date word
Interpretation of GEMDOS
Bit Number Description
0-4 Day
5-8 Month
9-15 Year - 1980
Results
None
See also
Tgetdate(), Tgettime(), Tsettime()
260
Tsetdate
Set GEMDOS Date
A 16-bit code that specifies the GEMDOS
date.
date:
Range
1-31
1-12
0-119
Opcode = 43 ($2B)