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Old February 7th, 2018, 06:21 AM   #1
Ece
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MVI56E-MNETC Read and write coils

Dear all,

I am working a project with 1 MVI56E-MNETC card and I am forcing a problem with read and write coils.
Regarding holding registers I am ok. I can write and read but when I am trying to read coils with internal address 1000 I can not read, but if I am trying to read the same coils with internal address 0 I can write. But I should read (and also write) coils not only in internal address 1000, but also in other addresses. Why have I this limitation?

PS : My internal address array has 6000 HR length.

Regards
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Old February 7th, 2018, 10:01 AM   #2
Ken Roach
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For other's reference: the MVI56E-MNETC is a modern version of the classic Prosoft Modbus card for ControlLogix.

The "MVI56E" means it's one of the 2nd generation Enhanced cards that can be configured across the backplane or over the network (older ones used the serial console port). MNET means Modbus/TCP, and the "C" means it's the Multi-Client model. So this is the highest-functionality member of the product family.

Ece, is your module acting as a Client (making requests) or a Server (answering requests) ?

In general, Modbus "coils" are considered binary Output data, so I'm not too surprised that you are seeing a discrepancy between their ability to be written versus being read.

The internal offset in the 6000-word flat data file inside the Prosoft module isn't as important as the way that each Modbus function (inputs, coils, internals, holding) are configured to interface with that data file.

Whatever additional details you can provide will help folks understand the issue.
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Old February 8th, 2018, 02:04 AM   #3
Ece
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Please let me to explain you my problem:
I have a device (Flow Computer - using Modbus TCP/IP) and I would like to read and write data for my ControlLogix PLC.
For this reason I am using a MVI56E-MNETC card. So, about the holding register I am ok. I have already storage these into MNET internal database [0-990] (also find attached). So, I am ready to read the coils. The Flow Computer storage the coils in address 38000. So, I would like to storage these coils into MNETC internal database in the address 995. For this reason I am writing the command for 0XCoils (find attached) but without result. The same job I should do in order to write coils (no result again).
Unfortunately, I created a new MNETC program in order to read coils but with internal address 0 (and not 995). The result was to read this coils without problem. So, I understood that I can read only if I used internal address 0. This is not acceptable for me because I would like to storage coils in different internal addresses.
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Old February 8th, 2018, 10:06 AM   #4
Ken Roach
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Thank you for the additional information !

To attach files to your post, compress them as ZIP files and use the Attach function.

I think you need to clarify whether you are reading Digital Output Coils or reading "Analog Input Registers". Modbus can be very confusing because the first digit (0,1,3,4) usually is used to indicate the data type (digital output coil, digital input contact, analog input, analog output/holding).

An address of "38000" suggests you are reading an Analog Input Register (3) with offset 8000.
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Old February 9th, 2018, 06:29 AM   #5
nhatsen
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Off the top of my head, if you want to work with coils & inputs you need to reserve the space in the read/write registers. Look for output offset, bit input offset, holding register offset and word input offset in the manual.
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