Free sourceforge.net/projects/qmodmaster/ Nice interface but only works with single register values (no float, ASCII strings etc support) https://github.com/SciFiDryer/ModbusMechanic GUI tool for reading and testing MODBUS TCP and RTU instruments. https://www.scadacore.com/tools/programming-calculators/online-hex-converter/ Handy for converting values Paid simplymodbus.ca/RTUmaster.htm Poor operation in Windows 7 but does actually work and does support multi register values so actually a very handy app and […]
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Function 16 Write Multiple Registers
Modbus RTU Function 16 'Preset Multiple Registers' To write 3 words (48 bits) to 3 consecutive registers you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message Type (0x10) Byte 2 Start Register Number (high byte) Byte 3 Start Register Number (low byte) Byte 4 Number of registers to write(high byte) […]
Function 06 Write Single Register
Modbus RTU Function 06 'Preset Single Register' To write a word (16 bits) to a register you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message Type (0x06) Byte 2 Register Number (high byte) Byte 3 Register Number (low byte) Byte 4 Data0 Byte 5 Data1 Byte […]
Function 03 Read Holding Registers
Modbus RTU Function 03 'Read Holding Registers' To read a word (16 bits) from a register you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message Type (0x03) Byte 2 Register Number (high byte) Byte 3 Register Number (low byte) Byte 4 Data Length (high byte, specified […]
Modbus Comms General
Resources modbus.org Modbus Application Protocol Describes function codes modbus.org Modbus over Serial Line Specification and Implementation Guide Register Addressing The Modbus register number should really be thought of as an offset rather than an address, as different vendors can use different register addressing schemes. Firstly registers may start from 0 for some devices and 1 for others. The register addressing […]
Modbus TCP/IP
Resources Acromag Introduction To Modbus TCP/IP Has a good explanation of how a RTU serial packet is transferred over TCP/IP modbus.org Modbus Messaging On TCP/IP Implementation Guide Simply Modbus TCP Page Open Modbus/TCP Specification
USB HID Report Descriptors
USB Org resources The full spec and downloadable tables etc can be found here (Device Class Definition for HID). Get the 'HID descriptor tool' from the same page to help create descriptors – very handy!!! Overview A USB HID Report Descriptor is requested by a USB host from a USB device. It tells the host […]
Breadboard
Capacitance between breadboard contacts EEVblog Dave answered this question in the episode here. The quick answer is that for a pair of 5 contact strips next to each other the capacitance between them was close to 2pF across a range of difference boards. Jumping a strip, so you leave an empty one in the middle, halved the capacitance. […]
Potentiometers & Potential Dividers
Potentiometer Input Impedance For AtoD Inputs This is based on the discussion found here. AtoD inputs will be specified with a maximum source resistance for them to function correctly to all of their specifications. The source resistance of a pot is highest at its midpoint setting, but even at that position it is only 1/4 of […]
Relay Contact Materials
Hard Silver Ag[97-98%], Cu+Ni General application relays. The copper and nickel contents give hardness. Long contact life, but tends to oxidise at higher temperatures. Silver Nickel AgNi A good standard contact material. More resistant to welding at high loads than hard silver. High burnout resistance. Silver Cadmium Oxide AgCdO More resistant to welding at […]