Timmers

Could someone tell me about the timmers for allen bradley plc the timmers has dn and en one the out side explain this operation or a example please forgive me I am new at this.

The EN bit is timer enabled. This bit is true when the logic to the left of the timer is true. The DN bit is timer done. This bit is true then the timer acc value it equal to the pre value. And there is also a TT bit which is timer timing. This bit is true then the timer is enabled bu the acc value has not reached the pre value.

Each of these bits are available for the programmer to use in the logic.

All of these can be seen in the T4 data table.

I hope that this answers your question.

Good reply by KMG.
I would like to add that the action of the DN bit is a little different between on delay timer (TON) instructions and off delay timer (TOF) instructions. KMG describes the on delay action correctly. With an off delay timer the DN bit comes on immediately when the logic to the left of the timer is true. It stays on for the timer preset time after the logic to the left of the timer goes false. Also, the timer doesn't start timing until the leading logic is false, so the timer timing bit (TT) is on from the time the leading logic goes false until the timer accumulated value reaches the preset.

Keith

timers

You should contact your nearest Allen-Bradley distributor and request the SLC500 Instruction Set manual. The publication number is 1747-RM001C-EN-P Sept. 2001. Or, go to AB.com and click on manuals online, click on control processors, click on SLC500 programmable controllers and then find the pub number and right click on that and save it to your hard drive. If you use dial-up ISP, then take a trip to town or go to a movie cause the manual is a 6.5 meg download. If you have DSL or other high speed ISP, you are in luck and will only have to invest a few mins in the download. This maunal will explain every thing you need to know about the AB SLC and MicroLogix family of PLCs.
Randy L.

p.s. This is a reprint from my reply to your other question about AB SLC programming instructions and the meaning of such things as EN, DN and bit numbers below the instruction.

SLC500 instruction set

This may also help you some:

http://www.geocities.com/plc_guide/index.html

Randy L.