Latched registers problem

[WKla]

Hello. I use an FX1N PLC. I have a project were I use latched (EEPROM backed-up) data registers. The problem is that some of the registers, 9 integers from D150 to D158, are set to the value 8447 during the execution of the program. This happens at random times (1-2 days). These registers are used only for storing parameters and they are set by the user through the HMI. Thank you.

[JRoss]

Make sure they aren't the upper half of a "double" (32-bit) register.

[Goody]

Jross's answer is almost certainly right and a trap that many fall into 32 bit numbers take up two consequitve data registers and the 2nd one will often read like nonesense. Check your program for this or the data being written from another source

[WKla]

I have checked for DINT (32 bit) registers but this is not the problem. The data registers are set through the HMI and remain like that 1-2 days. After this time these registers are set by the PLC like that: D150=D151=D152=D153= ... =D158=8447 (0x20FF). This happened to me 3 times and each time the registers are set to the same value (8447). How the EEPROM backed-up registers behave, if they are written over 10000 times? The PLC was used in another project before.

[JRoss]

The FX1N uses RAM for the working data and flash based memory for backing up data, so EEPROM isn't the problem. Also, the registers in the range you are identifying aren't backed up, typically. What HMI are you using? Also, if you would post your code, we could take a look at it for you.

[Sergei Troizky]

D128 and higher are latched registers in FX1N (aka backed up, aka holding). Writing cycles should not be an issue from my experience: I used to rewrite them in every scan and no unit failed after years of operation. I would disconnect the HMI over weekend for diagnostics and then read registers from PC. Anyways, it would be good to see the program. Is there any indirect addressing? Edited December 11, 2007 by Sergei Troizky

[JRoss]

Should have checked my manual... Thanks Sergei. I've been using the FX3U lately, which comes with D0-D199 non-latched as the factory default.

[WKla]

That looks to be the problem. I used D150 register with index register in a subroutine. When browsing the registers (GX IEC Dev: Project>Browse) it looks like it can't find the registers when they are composed like this: D100V1 or K4M100. Thank you. Edited December 14, 2007 by WKla

[Sergei Troizky]

It must read "If the PLC has been powered up for five minutes or more...". Mentioned 10000 cycles is guaranteed quantity, not necessarily the limit. Chance is, 10000 power ups will affect the entire unit life much more. And 10000 is 10 times a day during 3 years. Edited December 17, 2007 by Sergei Troizky

[vaibhav]

which mmi is used by you? if you are using E-1000 MMI with old OS, then that can be the problem bye

[Goody]