GFK-0467K Chapter 4 Series 90-30/20/Micro Instructions Set 4-7
4
Retentive SET Coil —(SM)— Retentive SET and RESET coils are similar to SET and RESET coils, but they are retained across
power failure or when the PLC transitions from STOP to RUN mode. A retentive SET coil sets a
discrete reference ON if the coil receives power flow. The reference remains ON until reset by a
retentive RESET coil.
Retentive SET coils write an undefined result to the transition bit for the given reference. (Refer to
the information on “Transitions and Overrides” in chapter 2, “System Operation.”)
Retentive RESET Coil —(RM)— This coil sets a discrete reference OFF if it receives power flow. The reference remains OFF until
set by a retentive SET coil. The state of this coil is retained across power failure or when the PLC
transitions from STOP to RUN mode.
Retentive RESET coils write an undefined result to the transition bit for the given reference. (Refer
to the information on “Transitions and Overrides” in chapter 2, “System Operation.”)
Links Horizontal and vertical links are used to connect elements of a line of ladder logic between
functions. Their purpose is to complete the flow of logic (“power”) from left to right in a line of
logic.
Note
You can not use a horizontal link to tie a function or coil to the left power rail.
You can, however, use %S7, the AWL_ON (always on) system bit with a
normally open contact tied to the power rail to call a function every sweep.
Example:
In the following example, two horizontal links are used to connect contacts E2 and E5. A vertical
link is used to connect contacts E3, E6, E7, E8, and E9 to E2.
|
|
| E2 E5 E1
|——| |——+———————+———————+——| |—————————————————————————————————————————————(/)—
| |
| |
| E3 E6 E7 |
|——| |——+——|/|——+——| |——+
| | | |
| | | |
| | E8 | E9 |
| +——| |——+——| |——+
|