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

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

Cortex

Davicom’s 3^rd 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 1^st MEXM-1
  • 1MA01 to 1MA24, 1MD01 to 1MD24 and 1MR01 to 1MR24
• And on the 2^nd 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 2^nd 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.