# PLC status bits for Allen-Bradley Control- Logix PLCs

**URL:** <https://forumautomation.com/t/plc-status-bits-for-allen-bradley-control-logix-plcs/3103>\
**Category:** PLC (Programmable Logic Controllers)\
**Tags:** interviewquestions\
**Created:** [February 6, 2018, 6:53pm UTC](https://forumautomation.com/t/plc-status-bits-for-allen-bradley-control-logix-plcs/3103 "2018-02-06T18:53:46Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![sivaranjith](https://forumautomation.com/letter_avatar_proxy/v4/letter/s/ba9def/32.png) [@sivaranjith](https://forumautomation.com/u/sivaranjith)\
**Post date:** [February 6, 2018, 6:53pm UTC](https://forumautomation.com/t/plc-status-bits-for-allen-bradley-control-logix-plcs/3103/1 "2018-02-06T18:53:47Z")

</div>

> ## What is a Status register?

A status register is a hardware register which contains the information about the status of the processor. It is a collection of flags bits in a Programmable status word. Status memory allows a program to check the PLC operation, and also make some changes.

Here we discuss the PLC status bits of Allen-Bradley Control-Logix PLCs. More complete lists are available in the manuals. The first six bits are commonly used and are given simple designations for use with simple ladder logic. More advanced instructions require the use of Get System Value (GSV) and Set System Value (SSV) functions.

> **Immediately accessible status values:**

**S:FS** - First Scan Flag **S:N** - The last calculation resulted in a negative value **S:Z** - The last calculation resulted in a zero **S:V** - The last calculation resulted in an overflow **S:C** - The last calculation resulted in a carry **S:MINOR** - A minor (non-critical/recoverable) error has occurred

> ## A selected list of status bits is shown below for Allen-Bradley Micrologic

**S2:0/0** carry in math operation

**S2:0/1** overflow in math operation

**S2:0/2** zero in math operation

**S2:0/3** sign in math operation

**S2:1/15** first scan of program file

**S2:8** the scan time (ms)

**S2:18** year

**S2:19** month

**S2:20** day

**S2:21** hour

**S2:22** minute

**S2:23** second

**S2:28** watchdog setpoint

**S2:29** fault routine file number

**S2:30 STI** (selectable timed interrupt) setpoint

**S2:31 STI** file number

**S2:46-S2:54,S2:55-S2:56 PII** (Programmable Input Interrupt) settings

**S2:55 STI** last scan time (ms)

**S2:77** communication scan time (ms)

> **Examples of SOME values available using the GSV and SSV functions:**

**CONTROLLERDEVICE** - information about the PLC

**PROGRAM** - information about the program running

LastScanTime MaxScanTime TASK EnableTimeout LastScanTime MaxScanTime Priority StartTime Watchdog

**WALLCLOCKTIM** E - the current time

DateTime DINT[0] - year DINT[1] - month 1=january DINT[2] - day 1 to 31 DINT[3] - hour 0 to 24 DINT[4] - minute 0 to 59 DINT[5] - second 0 to 59 DINT[6] - microseconds 0 to 999,999

to know more about [PROGRAMMING LOGIC DEVICES (PLC)](https://automationforum.co/2018/02/programming-logic-devices-plc.html)