Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 156)

Chapter
Statements 11
11 -4
Use the CLOCK0 (zero) statement to disable or turn off the free running
clock resident on the BASIC module. After you execute CLOCK0, the
special function operator TIME (page 9 -19) no longer increments.
CLOCK0 is the only module statement that can disable the free running
clock. CLEAR (page 11 -2) and CLEARI (page 11 -3) do not disable
the free running clock, only its associated ONTIME interrupt (page
11 -25).
Important: CLOCK0 and CLOCK1 (page 11 -5) are independent of the
clock/calendar.
You can also use CLOCK0 in Command mode.
Syntax
CLOCK0
Example
READY
>CLOCK0
CLOCK0