Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 107)

Using Basic Instructions
6–9
Timer Accuracy
Timer accuracy refers to the length of time between the moment a timer instruction
is enabled and the moment the timed interval is complete.
Timing accuracy is –0.01 to
+
0 seconds, with a program scan of up to 2.5 seconds.
The 1-second timer maintains accuracy with a program scan of up to 1.5 seconds. If
your programs can exceed 1.5 or 2.5 seconds, repeat the timer instruction rung so
that the rung is scanned within these limits.
Note Timing could be inaccurate if Jump (JMP), Label (LBL), Jump to Subroutine (JSR),
or Subroutine (SBR) instructions skip over the rung containing a timer instruction
while the timer is timing. If the skip duration is within 2.5 seconds, no time will be
lost; if the skip duration exceeds 2.5 seconds, an undetectable timing error occurs.
When using subroutines, a timer must be executed at least every 2.5 seconds to
prevent a timing error.
Addressing Structure
Address bits and words using the format Tf:e.s/b
Format Explanation
T Timer file
f File number. The only valid file number is 4.
: Element delimiter
Tf:e
e
Element
number Ranges from 0 – 39. These are 3-word elements. See figure on
page 6–8.
Tf:e
. Word element
s subelement
/ Delimiter
b bit
Programming