Understanding the number of Modbus I/O’s useable with different Davicom units

Davicom’s 2nd and 3rd generations of products have different capabilities with respect to the number of Modbus I/O points they can accommodate. 

Cortex

Davicom’s 3rd generation of products can accept a maximum of 256 I/O points for each type IE, it can take readings from up to 256 Analog inputs, 256 Digital inputs and it can control up to 256 Relay outputs. 

These I/O points can be distributed amongst 8 Modbus slaves, for standard units, and optionally, up to 16 or even 32 slaves. Furthermore, each slave can have a maximum of 99 I/O points of each type. 

These are identified by the following nomenclature in the Davicom Configuration files: 

xMAyy 

where:

  • x is the ID number of the slave (from 1 to 8 and optionally 16 or 32) 
  • MA stands for Modbus Analog (input)
  • For the Digital inputs, MA is replaced by MD (Modbus Digital)
  • For the Relay outputs, MA is replaced by MR (Modbus Relay)
  • yy is the sequential number of the I/O point (from 1 to 99)

For example, when using 2 of our MEXM-1 Modbus expansion modules (which each have 24 Analog inputs, 24 Digital inputs and 24 Relay outputs), the following I/O Identifiers would be available:

  • On the st MEXM-1
    • 1MA01 to 1MA24, 1MD01 to 1MD24 and 1MR01 to 1MR24
  • And on the 2nd MEXM-1
    • 2MA01 to 2MA24, 2MD01 to 2MD24 and 2MR01 to 2MR24
  • If 8 MEXM-1 modules are connected, the last one would have:
  • 8MA01 to 8MA24, 8MD01 to 8MD24 and 8MR01 to 8MR24, for a grand total of 192 Analog inputs, 192 Digital inputs and 192 Relay outputs.

The advantage of having different Modbus slave devices instead of having all the I/O’s in the same slave is to allow them to be physically distributed at different locations around a site, or to be completely different devices. For example, a kWh measuring device, an electrical generator or an HVAC unit.

DV-200

Davicom’s 2nd generation of products can accommodate less Modbus I/O points than the Cortex Series, and there are certain other limitations.

The maximum number of Modbus I/O’s is listed below: 

  • Analog inputs: 128
  • Digital inputs in Modbus TCP mode:192
  • Digital inputs in Modbus RTU mode:168
  • Relay outputs: 72
  • Number of slaves in Modbus TCP mode: 8 (Ex: 1MA01 to 8MA01) 
  • Number of slaves in Modbus RTU mode: 7 (Ex: 1MA01 to 7MA01)

No optional upgrades exist to increase the number of slaves above 8, or 7, depending on the mode.

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