B ehr Systems (Auburn Hills, Mich.) had to find a way to provide tight connection to the human-machine interface display located 2,000 feet from the controller on its paint line. The system includes custom software running on a VME single-board computer controlling paint amount and airflow with a VME-based Allen-Bradley PLC for automation control. Added memory in the system holds process data.
HMI for the system is developed in Visual Basic running on Microsoft Windows NT. It exposes process data to operators and allows parameter setting for different batches. The monitor and keyboard must be located remotely from the processor. The solution had been a ‘black box’ that was prone to failure.
Behr Systems software engineer, Dave Monacelli, solved the problem when he discovered the Model 618 bus-to-bus adapter from SBS Technologies, Connectivity Products (formerly bit3, St. Paul, Minn.). Model 618 is a PCI bus card for a personal computer with a fiber optic connection. Eliminating keyboard, mouse, and video extenders, it allows the PC to act as if it were a single-board computer in the remote VME rack.
The card translates PCI bus signals into VME bus signals. Data transfer does not involve any VME processors since the built-in DMA controller sends and receives interrupts. The card comes with CD-ROM containing software drivers for such popular operating systems as Windows, QNX, Solaris, and VxWorks. This handy feature eliminates the need to rewrite applications to apply the solution.
Another benefit of this solution lies in bringing the latest microprocessors to VME through the card. Further, if the VME system power must be cycled on and off frequently say to add or remove a card, the processor need not be shut down. A dual-port RAM daughter card sits between PC and VME as a data path to which each side can read and write independently so neither takes bandwidth from the other.
Model 618 provides two methods of intersystem communication: memory mapping and Direct Memory Access (DMA). Memory mapping controls random access (PIO) transfers. Random access reads and writes from the PCI system to the VMEbus, from the PCI bus to optional dual port RAM, and from the VMEbus to the PCI bus are supported. The adapter provides flexible mapping of PCI bus address space to VMEbus memory and I/O address space.
Controller Mode DMA and Slave Mode DMA are supported. Both DMA modes support Dual Port RAM and 32-bit Block Mode transfers. Controller Mode DMA also supports 16-bit Block Mode Transfers. DMA transfers from chassis to chassis are at sustained rates above 26M Bytes/sec. Byte swapping and word swapping functions are provided. The VMEbus adapter card meets IEEE 1014C specifications. The PCI adapter card conforms to PCI Local Bus Specification 2.0.
Behr Systems now can run its HMI from the remote area without the errors and complications found previously.
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