Allen-Bradley 1785-KA3 Communication Adapter Module
The Allen-Bradley 1785-KA3 is a PLC-2 family communication adapter interface module that links PLC-2 series programmable controllers to a Data Highway Plus (DH+) network. Installed in any slot (except the leftmost slot) of a standard 1771 I/O chassis, it enables data exchange, programming, and monitoring across industrial networks. The module draws 1.2 A at 5 VDC from the backplane and requires no external power supply.
Network Connections and Interfaces
The 1785-KA3 features dedicated interface ports that support Data Highway, Data Highway Plus, and 1784 Series Industrial Terminals (such as the 1784-T50 workstation). When installed alongside a compatible PLC-5 system, it connects directly to Channel 3 of the PLC-5 processor. Up to four 1785-KA3 modules can be deployed per system to expand multi-node network architectures.
Hardware Configuration and Backplane Keying
Module operation and network node identification are configured using three onboard switch assemblies: the DH+ baud rate assembly, the write options assembly, and the node address group switch. To ensure proper physical alignment and prevent incorrect slot placement, the module is keyed to the 1771 backplane connector between pins 4 and 6, and pins 22 and 24 of the upper connector. Front-panel status LEDs provide independent diagnostic monitoring for each communication channel.
| Parameter | Specification |
|---|---|
| Brand | Allen-Bradley |
| Model | 1785-KA3 |
| Product Type | Communication Adapter Interface Modules |
| Series | PLC-2 / PLC-5 Compatible |
| Interface Ports | Data Highway, Data Highway Plus (DH+), 1784 Industrial Terminal |
| PLC-5 Processor Connection | Direct Connection to Channel 3 |
| Backplane Power Requirement | 1.2 A at 5 VDC |
| Required External Power | None |
| Maximum Modules Per System | 4 |
| Wiring Arm | 1771-WN |
| Coating | Conformal coat |
| Operating Temperature | 0 to 60 deg C (32 to 140 deg F) |
| Storage Temperature | -40 to 85 deg C (-40 to 185 deg F) |
| Relative Humidity | 5% to 95% non-condensing |
| Weight | 0.85 kg (1.88 lbs) |
Frequently Asked Questions
Q: Where should the 1785-KA3 module be installed within the 1771 I/O chassis?
A: The module can be installed in any available slot of the 1771 I/O chassis except the furthest left slot, which is reserved for the primary processor or adapter.
Q: How is the node address and network communication configured on the 1785-KA3?
A: Communication settings are established using three onboard DIP switch assemblies: the DH+ baud rate switch assembly, the write options switch assembly, and the node address group switch assembly.
Q: How is the 1785-KA3 keyed to prevent incorrect insertion into the backplane?
A: Keying positioning bands must be placed between pins 4 and 6, and pins 22 and 24 of the top backplane connector.
Allen-Bradley 1785-KA3 Communication Adapter Module
Allen-Bradley 1785-KA3 Communication Adapter Module
The Allen-Bradley 1785-KA3 is a PLC-2 family communication adapter interface module that links PLC-2 series programmable controllers to a Data Highway Plus (DH+) network. Installed in any slot (except the leftmost slot) of a standard 1771 I/O chassis, it enables data exchange, programming, and monitoring across industrial networks. The module draws 1.2 A at 5 VDC from the backplane and requires no external power supply.
Network Connections and Interfaces
The 1785-KA3 features dedicated interface ports that support Data Highway, Data Highway Plus, and 1784 Series Industrial Terminals (such as the 1784-T50 workstation). When installed alongside a compatible PLC-5 system, it connects directly to Channel 3 of the PLC-5 processor. Up to four 1785-KA3 modules can be deployed per system to expand multi-node network architectures.
Hardware Configuration and Backplane Keying
Module operation and network node identification are configured using three onboard switch assemblies: the DH+ baud rate assembly, the write options assembly, and the node address group switch. To ensure proper physical alignment and prevent incorrect slot placement, the module is keyed to the 1771 backplane connector between pins 4 and 6, and pins 22 and 24 of the upper connector. Front-panel status LEDs provide independent diagnostic monitoring for each communication channel.
| Parameter | Specification |
|---|---|
| Brand | Allen-Bradley |
| Model | 1785-KA3 |
| Product Type | Communication Adapter Interface Modules |
| Series | PLC-2 / PLC-5 Compatible |
| Interface Ports | Data Highway, Data Highway Plus (DH+), 1784 Industrial Terminal |
| PLC-5 Processor Connection | Direct Connection to Channel 3 |
| Backplane Power Requirement | 1.2 A at 5 VDC |
| Required External Power | None |
| Maximum Modules Per System | 4 |
| Wiring Arm | 1771-WN |
| Coating | Conformal coat |
| Operating Temperature | 0 to 60 deg C (32 to 140 deg F) |
| Storage Temperature | -40 to 85 deg C (-40 to 185 deg F) |
| Relative Humidity | 5% to 95% non-condensing |
| Weight | 0.85 kg (1.88 lbs) |
Frequently Asked Questions
Q: Where should the 1785-KA3 module be installed within the 1771 I/O chassis?
A: The module can be installed in any available slot of the 1771 I/O chassis except the furthest left slot, which is reserved for the primary processor or adapter.
Q: How is the node address and network communication configured on the 1785-KA3?
A: Communication settings are established using three onboard DIP switch assemblies: the DH+ baud rate switch assembly, the write options switch assembly, and the node address group switch assembly.
Q: How is the 1785-KA3 keyed to prevent incorrect insertion into the backplane?
A: Keying positioning bands must be placed between pins 4 and 6, and pins 22 and 24 of the top backplane connector.
