Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | 1771-DB |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Product Type | BASIC Coprocessor Module |
| Compatible Platforms | PLC-2, PLC-3, PLC-5 (1771 I/O system) |
| Programming Language | BASIC-52 (Intel), additional C support |
| User Memory | 24 KB available (32 KB battery-backed RAM total) |
| Serial Ports | 2 independent ports (PRT1, PRT2) |
| Communication Protocols | RS-232-C, RS-422-A, RS-485, DH-485 |
| Communication Rate | 300–19.2 Kbps |
| PLC Interface | Block-transfer (BTR/BTW) |
| Scan Time | 1.3–5 ms |
| Isolation Voltage | 500V DC port-to-port and port-to-backplane |
| Backplane Current | 0.75A (with DH-485 device) / 0.65A (without) |
| Real-Time Clock | Time-of-day, 10 ms resolution |
| Power Dissipation | 4W maximum |
| Wiring Arm | 1771-WN |
| Weight (Approx) | 0.37 kg |
Main Features and Advantages
Independent processing power offloads the PLC: The 1771-DB executes BASIC programs autonomously, freeing the host PLC processor from complex math routines, string handling, and data formatting tasks that consume scan time and memory in ladder logic. A PLC-5 processor communicating with the 1771-DB via block-transfer need only send and receive data words; the actual computation, decision logic, and report formatting occur within the module’s own 24 KB user memory. This architecture is particularly valuable in legacy installations where processor memory is constrained or scan time is critical, allowing existing control systems to gain advanced computational capability without a controller upgrade.
Multi-protocol serial connectivity for diverse peripherals: The 1771-DB‘s two serial ports can be independently configured for RS-232-C, RS-422-A, or RS-485 operation, with DH-485 support available for network integration. This flexibility enables simultaneous connection of a programming terminal, a serial printer for report generation, and a remote modem or host computer. The DH-485 port allows the 1771-DB to communicate with remote SLC processors or other DH-485 devices, extending its reach beyond the local I/O chassis. Communication rates from 300 to 19.2 Kbps accommodate both legacy slow-speed devices and faster modern peripherals.
Built-in memory expansion and programmability: The 1771-DB accepts optional EEPROM memory modules (1771-DBMEM1 for 8 KB or 1771-DBMEM2 for 32 KB) for non-volatile program storage, eliminating the need to reload BASIC programs after battery depletion or module replacement . The module supports a comprehensive BASIC instruction set including FOR-NEXT loops, GOSUB subroutines, string handling, and mathematical functions, along with specialized backplane CALL macros for block-transfer operations and data format conversion between BASIC floating-point and PLC data types . This programming environment allows engineers to implement custom algorithms, data logging routines, and communication protocols tailored to specific application
