Appendix A
Appendix D
Special Relays
D–2
Special Relays
DL05 PLC Special Relays
“Special Relays” are just contacts that are set by the CPU operating system to
indicate a particular system event has occurred. These contacts are available for
use in your ladder program. Knowing just the right special relay contact to use for a
particular situation can save lot of programming time. Since the CPU operating
system sets and clears special relay contacts, the ladder program only has to use
them as inputs in ladder logic.
SP0 First scan on for the first scan after a power cycle or program to run transition
only. The relay is reset to off on the second scan. It is useful where a
function needs to be performed only on program startup.
SP1 Always ON provides a contact to insure an instruction is executed every scan.
SP3 1 minute clock on for 30 seconds and off for 30 seconds.
SP4 1 second clock on for 0.5 second and off for 0.5 second.
SP5 100 ms clock on for 50 ms. and off for 50 ms.
SP6 50 ms clock on for 25 ms. and off for 25 ms.
SP7 Alternate scan on every other scan.
SP11 Forced run
mode
on when the mode switch is in the run position and the CPU is
running.
SP12 Terminal
run mode
on when the CPU is in the run mode.
SP13 Test
run mode
on when the CPU is in the test run mode.
SP15 Test
stop mode
on when the CPU is in the test stop mode.
SP16 Terminal
PGM mode
on when the mode switch is the the TERM position and the CPU is in
program mode.
SP17 Forced stop on when the mode switch is in the STOP position.
SP20 Forced
stop mode
on when the STOP instruction is executed.
SP22 Interrupt enabled on when interrupts have been enabled using the ENI instruction.
Startup and
Real-Time Relays
CPU Status Relays
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