Honeywell 30751044-008 ROM PLC Control Board
The Honeywell 30751044-008 is a printed circuit board assembly used in Honeywell’s PLC and process control systems (possibly Series 9000 or HC900). This board is designated as a ROM card (read-only memory) containing control firmware and configuration data. The board carries UL 94V-0 flammability rating on its substrate and is revision 1. It is designed for installation in a Honeywell controller rack or chassis.
Hardware Description
The board dimensions are approximately 160 mm x 200 mm. It has two 28-pin DIP sockets populated with EPROMs (UV erasable) or masked ROMs (type: 27C512, 64 KB each). A 16-bit microcontroller (Motorola 68HC11) runs at 8 MHz. Additionally, there are 32 KB SRAM (battery backed by a lithium coin cell) and a Xilinx CPLD (XC9572) for address decoding. The board has 8 jumper headers for configuration options (I/O mapping, bus termination).
Connectors and Interface
The board connects to the backplane via a 96-pin DIN 41612 connector (type C). It also provides an external 10-pin header for a diagnostic LED panel and a 4-pin header for an external battery. A 9-pin D-sub (RS-232) is mounted on the bracket for service communication (9600 bps, uses proprietary Honeywell protocol).
Power and Environment
Power: +5V DC (1.5 A) and +12V (0.2 A) derived from the backplane. Power consumption: 8 W. Operating temperature: 0 to 60°C; storage: -40 to 85°C. Humidity: 20% to 80% non-condensing. The board is conformally coated (acrylic) to protect against dust and mild corrosives. The substrate material is FR-4, UL 94V-0 certified.
Firmware and ROM Contents
The board’s ROM contains the operating system (Honeywell Control Executive) and the user’s compiled control strategy. The EPROMs can be replaced by the user if the firmware is updated. A write-protect jumper prevents accidental erasure. The board also contains a real-time clock (RTC) with a 3V lithium battery (CR2032).
Diagnostics and LED
A single green LED (PWR) indicates power; a red LED (FAIL) signals watchdog timeout or ROM checksum error. A 4-bit DIP switch selects the board address (1–15) on the backplane bus. An optional external test point (TP1) allows monitoring of the +5V rail.
Compatibility and Application
This board is compatible with Honeywell 9000 series I/O racks and the HC900 hybrid controller. It is typically used as the main CPU or as a communication gateway for remote I/O. It can be replaced in the field without special tools (except for EPROM programmer).
Ordering and Manual
Honeywell part number: 30751044-008. Rev.1 board. The board is sold as a spare part for legacy systems. Manual: Honeywell HC900 Control Board Guide (51-52-25-117). RoHS status: non-compliant (older board may contain lead in solder).
