If the data packet is being sent via Modbus RTU, the first character transmitted is the
slave address, and the last two characters are a CRC type checksum. If the data
packet is being sent via Modbus TCP, there is a TCP header at the beginning of the
packet, and the last byte of that packet is the same slave address or unit number that
would have been sent via RTU. The RTU checksum is not included because Ethernet
has its own checksum that covers the entire Ethernet transmission.
The process of translating RTU to TCP or vice versa is simply a matter of adding or
subtracting TCP header and RTU checksum. The only configuration required in this
type of gateway is to create an association between RTU slave addresses and
TCP IP addresses.
2.3 What is New in Model BB3-6101/MX-61
The BB3-6101 is a significant enhancement over its predecessor, the BB2-6010. The
MX-61 is the equivalent enhancement over its predecessor, the SPX. The hardware
includes a faster processor and hardware encryption engine for efficient rendering of
secure web pages. The software includes numerous enhancements.
IPv6 support
Secure (HTTPS) web server
Faster processor
Added features specific to the application
2.4 Connectors and Indicators
Follow these steps to make the initial connection to the BB3-6101/MX-61.
(a) Connect power. Apply +12VDC to +24VDC or 24VAC to the terminal marked
“POWER”, and common or ground to one of the terminals marked “GND”.
2. Connecting Gateway for the First Time
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