Question about Latch/Link Relays

[netdomain]

What are Latch and Link Relays in Mitsubishi? What are their functions? I thought they were like Latch bits in AB, but when I read Panic Mode's post, I realized that M are bits and I can use "Set & Reset" for Latch/Unlatch. So now I am wondering what can I do with Latch Relays? Anyone can help please?

[Crossbow]

Latch relays are battery backed, so once turned on, they will not lose their state on a power cycle of the PLC.

[Colin Carpenter]

Latch relay ranges are set up in the programming software and refer to relays that retain their state even after a power down / power up. In other words, their state is battery backed. In the old DOS MEDOC days, they showed as L coils when programming them, as compared to M coils which are not battery backed relays. I don't think the designation is quite as clear in the later software versions, though I'm not sure on that. M coils will normally retain their state in the PLC when downloading new software to the PLC, as long as the power is maintained. This is different to the AB SLC500 range, where the M Coil states (Data Tables in AB speak) is uploaded by RS Logix, remembered and then downloaded again to the SLC along with the programme code. Give me the Mitsubishi way any day on that one ... Link relays (B Coils) are used for networking, normally using the Melsec Net network cards. The range of B coils is also set up in the programming software. They can be defined as "Master to Slave" or "Slave to Master" (and others in a multi node network). When a "Master to Slave" B Coil is turned on in the Master, the same B Coil turns on in the slave, and vice versa for "Slave to Master" B Coils.

[Goody]

The L relay is in the A or Q plcs The FX range does not have L relays but they do have the equivalent in latching or memory retentive relays with certain pre designated M relays Usually M500 and above

[waynes]

You can adjust these ranges to M0-M1023. The default setting is M500-M1023 though...