SmartSwarm 300 Series
:
133
"address": 40,
"address_offset": 2,
"name": "Pump Command",
"alias": "",
"datatype": {
"enum_type": {
"num": [
0,
1
],
"val": [
"Normal Operation",
"Max Speed"
]
}
},
"length": 1,
"zero_value": null,
"max": null,
"min": null,
"scaling": null,
"units": "",
"state": "VALIDATED"
}
It is recommended that JSON maps be validated using an online JSON formatter. It is difficult to find errors,
especially when the maps contain a large number of registers.
17. APPENDIX 5 - BACKGROUND INFORMATION
17.1 MODBUS BACKGROUND
Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic
controllers (PLCs). The Modbus standard is currently managed by The Modbus Organization. The standard is
available for free download from
. Download the “Modbus Serial Line Protocol and
Implementation Guide” (Modbus_over_serial_line_V1_02.pdf) and the “MODBUS Protocol Specification”
(Modbus_Application_Protocol_V1_1b3.pdf)
Modbus is a simple request-response protocol, in which a master device sends a message asking for a particular
slave device to return a number of registers, each containing information collected or derived from the devices and
sensors connected to the slave.
It can be implemented over Serial (Modbus ASCII / Modbus RTU) or Ethernet (Modbus TCP/IP). "Modbus RTU"
(Remote Terminal Unit) uses raw binary encoding, whilst "Modbus ASCII" uses ASCII characters (7 bits). The
SmartSwarm 351 currently supports eavesdropping on serial Modbus RTU networks only.