ModbusRTU Master
Comms Port
Description Each Modbus RTU Master will have one Comms Port function block which provides global serial port configuration, control, and monitoring.
Availability
  • Available only in the dw2xx series products
  • Requires library: System & I/O
  • Requires: Modbus Master
  • Singleton function block
  • Firmware versions 0x2007 and later
savvy-SFD Graphic modbusPort5
Graphic with Parameters modbusPort5

Parameters

Comms Speed Internal Parameter, Read-write, Enumerated with Direct Entry (unsigned 16-bit integer)

The communications rate for the serial connection in bits per second (b/s) or kilobits per second (kb/s). The Comms Speed can be set between 100 b/s to 500 kb/s. Typical values are enumerated; however, the user may specify any value between the upper and lower limits.

For proper operation, the Comms Speed parameter MUST match the slave device's settings.

High-speed comms requires careful engineering of the cable, connections, termination, etc.


12 = 1.2 kb/s
24 = 2.4 kb/s
48 = 4.8 kb/s
96 = 9.6 kb/s
144 = 14.4 kb/s
192 = 19.2 kb/s
384 = 38.4 kb/s
576 = 57.6 kb/s
768 = 76.8 kb/s
1152 = 115.2 kb/s
2304 = 230.4 kb/s
Comms Configuration Internal Parameter, Read-write, Enumerated (unsigned 16-bit integer)

The character framing for the Modbus RTU serial connection in the format Data Bits-Parity-Stop Bits.
Character framing is specified as:
  • Data Bits - Fixed at 8 data bits.
  • Parity - Selectable as N (None), O (Odd), E (Even), S (Space = 0), or M (Mark =1).
  • Stop Bits - Selectable as 1, 1.5, or 2.

0 = 8-N-1
1 = 8-O-1
2 = 8-E-1
3 = 8-S-1
4 = 8-M-1
5 = 8-N-1.5
6 = 8-O-1.5
7 = 8-E-1.5
8 = 8-S-1.5
9 = 8-M-1.5
10 = 8-N-2
11 = 8-O-2
12 = 8-E-2
13 = 8-S-2
14 = 8-M-2
Comms Timeout Internal Parameter, Read-write, Analog (signed 16-bit integer)
2 ms to 30000 ms

The timeout sets the time the Modbus master is to wait for a reply from the current slave device before moving on to the next parameter in the polling list. The timeout must be adjusted appropriately for the installation and the type(s) of slave devices attached

Comms Timeout >> Request Time + Silence Time + Slave Latency + Response Time + Silence Time.
Status Output, Read-write, Enumerated (signed 16-bit integer)

This is the logical inclusive-OR of all the Last Error parameters in the Modbus RTU register function blocks. This parameter is updated once per poll cycle.

All individual Last Error codes can be reset by clicking on this parameter and applying the Reset command.


0 = OK
1 = Error
Enable Input, Read-write, Boolean (signed 16-bit integer)

A global parameter controlling serial communications through the EIA-485 port. When set to Disable, all polling is suspended.
0 = Disable
1 = Enable
Bandwidth Internal Parameter, Read-write, Analog (unsigned 16-bit integer)
10 % to 90 %

This parameter allocates the percentage of the available communciations bandwidth to be dedicated to the generic ModbusRTU Master function blocks. The remaining percentage of bandwidth is used to support the native device-level function blocks (e.g., blocks like the Motor Control function block in the dw213 smarty-o for the Optidrive Plus drive).
Actual Polling Period 'High' Internal Parameter, Read-only, Analog (signed 16-bit integer)
0.000 s to 32.767 s

This diagnostic displays how often parameters specified as a High priority by their associated function blocks are updated on the Modbus RTU comms link.

Generally, the round-robin polling scheduler prioritizes the parameters as follows:

ParameterUpdated
HighEach parameter is updated every polling cycle.
MediumOne Medium parameter is updated every polling cycle until the entire Medium polling list is traversed.
LowAfter the Medium list is traversed, one Low parameter is processed the next High cycle. Then, the Medium list is traversed again before updating the next Low parameter.

For example, for two High parameters (H1, H2), three Medium parameters (M1, M2, M3), and two Low parameters (L1, L2) the sequence would be.

H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L1,
H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L2


32767 = >32s
Actual Polling Period 'Medium' Internal Parameter, Read-only, Analog (signed 16-bit integer)
0.000 s to 32.767 s

This diagnostic displays how often parameters specified as a Medium priority by their associated function blocks are updated on the Modbus RTU comms link.

Generally, the round-robin polling scheduler prioritizes the parameters as follows:

ParameterUpdated
HighEach parameter is updated every polling cycle.
MediumOne Medium parameter is updated every polling cycle until the entire Medium polling list is traversed.
LowAfter the Medium list is traversed, one Low parameter is processed the next High cycle. Then, the Medium list is traversed again before updating the next Low parameter.

For example, for two High parameters (H1, H2), three Medium parameters (M1, M2, M3), and two Low parameters (L1, L2) the sequence would be.

H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L1,
H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L2


32767 = >32s
Actual Polling Period 'Low' Internal Parameter, Read-only, Analog (signed 16-bit integer)
0.000 s to 32.767 s

This diagnostic displays how often parameters specified as a Low priority by their associated function blocks are updated on the Modbus RTU comms link.

Generally, the round-robin polling scheduler prioritizes the parameters as follows:

ParameterUpdated
HighEach parameter is updated every polling cycle.
MediumOne Medium parameter is updated every polling cycle until the entire Medium polling list is traversed.
LowAfter the Medium list is traversed, one Low parameter is processed the next High cycle. Then, the Medium list is traversed again before updating the next Low parameter.

For example, for two High parameters (H1, H2), three Medium parameters (M1, M2, M3), and two Low parameters (L1, L2) the sequence would be.

H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L1,
H1, H2, M1, H1, H2, M2, H1, H2, M3, H1, H2, L2


32767 = >32s
Minimum Comms Silence Internal Parameter, Read-write, Analog (unsigned 16-bit integer)
0.00 ms to 10.00 ms

The Modbus RTU specification requires the communication link be silent (idle on-the-wire) at least 3.5 character times between packet transmissions. For bitrates exceeding 19.2 kb/s, the standard also recommends the idle time be extended by 1.75 ms. This parameter allows a larger silent time to be set if required for the associated slave devices.

The actual Comms Silence will be the greater of 3.5 character times or this parameter.

Note: Some ModbusRTU slaves do not require an extended silence. The communication link will be much more efficient with shorter silences, especially at higher bit rates.


0 = 3.5 Characters