Owner's manual
Table Of Contents
- Table of Contents
- Introduction
- SeaI/O Hardware Description
- SeaI/O Base and Expansion Modules
- SeaI/O Module Common Features
- SeaI/O Configurations & Specifications
- 410 Series – 16 Optically Isolated Inputs/16 Reed Relay Outputs
- 420 Series – 16 Optically Isolated Inputs/8 Form C Outputs
- 430 Series – 32 Optically Isolated Inputs
- 440 Series – 32 Reed Relay Outputs
- 450 Series – 16 Form C Relay Outputs
- 462 Series – 96 Channel TTL DB-78
- 463 Series – 96 Channel TTL 50-Pin
- 470 Series – 16 A/D, 2 D/A, 8 24V Outputs, 8 Isolated Inputs
- 520 Series – 8 Optically Isolated Inputs/8 High-Current Form C Outputs
- Power Options
- Hardware Configuration
- Wiring Options
- Mounting Options
- Accessories
- SeaMAX Application Suite
- SeaI/O Architecture
- Device Address Configuration
- Configuring the “Base” SeaI/O Module
- Configuring N-Series Expansion Modules
- Configuring an Ethernet Module (E-Series)
- MaxSSD Configuration & Diagnostics Utility
- Communicating Via Modbus
- Extended Modbus Command Set
- Developing Custom Applications Using SeaMAX API
- SeaMAX API
- Non Object-Oriented SeaMAX API
- IOCTL Calls and Functionality
- Using SeaMAX with Visual C++ 6.0
- Using SeaMAX with Visual Basic 6.0
- Example SeaMAX Programming Tasks
- CEthernet API
- Appendix A – Data Encoding Tables
- Appendix B – CRC Calculation
- Appendix C – SeaIO Model 462/463 Holding Register Set
- Appendix D – SeaMAX Data Types and Structures
- Appendix E – Troubleshooting
- Appendix F – How To Get Assistance
- Appendix G – Compliance Notices
- Warranty
© Sealevel Systems, Inc.
- 55 -
SeaI/O User Manual
Modbus RTU
The Modbus RTU specification is a serial line style of communication where the
packets are determined by a series of timeouts. The last byte of an arriving packet is
defined as no more bits have been clocked into the shift registers for 3.5 character
times (i.e., no more bytes have been received for at least 3.5 character times). The
layout of a Modbus RTU packet is shown below.
Address Payload CRC-16
The payload consists of function code, followed by the function specific data. That
data is well defined within the Modbus Application Protocol specification. The
extended commands, defined in this manual, are good examples of how the payload
of a Modbus command is designed.
Modbus TCP
The SeaI/O E-Series (Ethernet) modules utilize the Modbus TCP communications
package. The libraries provided with the SeaI/O modules will operate virtually the
same as the Modbus RTU libraries.
The Modbus TCP protocol is slightly easier to use because there is no CRC attached.
Instead, Modbus TCP relies on the TCP implementation to ensure the message gets
to the sender without error.
The defined port for Modbus TCP communications is 502. This port has been
reserved on TCP modules that implement Modbus TCP. All Ethernet enabled SeaI/O
modules support a bridging mode, where all connected modules can respond to
Modbus commands as if they were a single unit. The modules utilize their unique
Slave ID (Unit ID) and will respond to a command that the Ethernet bridge will then
transmit back to the user. The header of the TCP message is named the MBAP
Header, and is designed as follows:
Tx ID (h) Tx ID (l) Protocol ID (h) Protocol ID (l) Length (h) Length (l) Unit ID
Following the MBAP header is the same payload of the RTU messages described in
the Modbus Application Protocol Specification.