Allen-Bradley 1785-V80B PLC-5/V80 VME Processor

The 1785-V80B is a specialized PLC-5/V80 programmable logic controller designed for seamless, direct integration into a VMEbus architecture. Compliant with the C.1 VMEbus specification, this processor installs directly into a VMEbus backplane, allowing shared bus execution alongside other VMEbus CPU and I/O modules without separate system gateways. It retains the complete, powerful instruction set of the enhanced PLC-5/80 processor while expanding native execution through custom VME status files and extended message (MSG) instructions that handle cross-bus data transfers and hardware interrupt generation. Operating with 100 Kilowords of onboard battery-backed SRAM, the unit manages comprehensive industrial applications up to 2944 total I/O over dedicated DH+ and Universal Remote I/O links, complemented by an optically isolated RS-232-C serial engine for local programming and DF1 point-to-point topologies.

Ordering Information

• 1785-V80B
  • PLC-5/V80 VMEbus Programmable Logic Controller Processor, 100 kWord SRAM.

Revision Control

• 1785-V80B Ser A (Series A, Rev A)
• 1785-V80B Ser B (Series B, Rev B)
• 1785-V80B Ser C (Series C, Rev C)
• 1785-V80B Ser D (Series D, Rev D)
• 1785-V80B Ser E (Series E, Rev E)

Hardware Specifications

Engineering Notes

• VME Status File Access: Features an exclusive software-defined "VME status file" that enables ladder programs to explicitly monitor, evaluate, and modify low-level VMEbus system variables.
• Instruction Set Extensions: The standard ladder instruction block for messaging (MSG) is extended natively to command VMEbus data block transfers and issue structured backplane hardware interrupts.
• Code Portability: Program configurations and ladder logic files developed for the standard enhanced PLC-5/40 or PLC-5/80 platforms run directly on the 1785-V80B with matching execution baselines.
• SRAM Preservation: Because this hardware platform does not feature internal EEPROM burning options, an active backup battery asset is required on the backplane or processor assembly to protect logic data during power downcycles.

Field Guidelines

• Backplane Insertion: Verify the host VMEbus chassis power is fully switched off before inserting or extracting the processor card. Seat the multi-pin DIN backplane connectors straight into the card guide tracks to avoid pin misalignment.
• Channel 0 Connection: Pin assignments on the 25-pin D-shell serial interface match EIA RS-232-C protocols; ensure shielding braid is terminated to the connector hood to maintain the integrity of optical isolators under high noise conditions.
• Network Tuning: When configuring channels 1A, 1B, 2A, or 2B for Data Highway Plus (DH+) or Remote I/O, ensure the end-of-line termination resistors match the physical baud rate selected (e.g., 150 Ohm for 57.6 kbps or 82 Ohm for 230.4 kbps setups).
• Programming Access: Local workstation access is established via the two front-panel 8-pin mini-DIN peripheral connections or over the primary DH+ highway link.

Technical & Procurement FAQ

Q: Can a standard Allen-Bradley EEPROM module be inserted into the 1785-V80B for non-volatile backup?

A: No, the 1785-V80B VME processor does not incorporate sockets or system architecture to accept EEPROM memory modules.

Q: How are communication channels 1A, 1B, 2A, and 2B physically wired on the front panel?

A: Each of these four independent channels features a dedicated 3-pin phoenix-style terminal plug that can be individually configured for DH+, Remote I/O Scanner, or Remote I/O Adapter modes.

Q: Can this processor module drive standard local 1771 I/O chassis blocks?

A: It cannot drive local or extended local I/O chassis directly because it lacks extended local drive ports; all 1771 or external I/O hardware must be linked remotely over the universal remote I/O scanner networks or over the VMEbus backplane.