Product Description

The HYTEC VPI 3331 is a fast and efficient VME Controller for IBM PC/AT and compatible Hosts. The unit is designed to port slave VME I/O modules registers and memory areas into the Host’s address space. The interface is mapped into I/O space on the PC/AT and is compatible with System Board DMA controllers.

Major Features

Applications

• Easy–to–drive VME Test Station.
• VME Data Acquisition with ’familiar’ Host.
• VME Development Station supported by freely available DOS–based software development tools.

Description of Operation

The VPI 3331 uses 16 bit wide registers mapped directly into the PC’s I/O space to provide access to VME slave modules. Two 16 bit registers hold the VME address while another two transfer VME data. Address and data width are specified by the address modifier, which is pre–loaded into an 8 bit register.

Addressing the LOW data register (D00–D15) causes a VME cycle to take place (either Read or Write), whereupon the VPI 3331 arbitrates for the VME bus and does the cycle. Failure to complete is flagged by BUS ERROR in the Control and Status Register, also accessible from the PC, which also contains Interrupt Enable and Interrupt Flag bits.

Interrupts are handled by first hardware selecting the IRQ line in VME which the 3331 will monitor, then patching that through to a PC System Board IRQ line. The Host’s response will be to read the 3331 Interrupt Handling Register which causes an Interrupt Acknowledge cycle to be performed to the interrupting slave, yielding an 8 bit ID/Status byte for the processor.

DMA Access to the 3331 is by setting up a spare channel on a System Board DMA Controller and enabling the 3331 DMA Request Flag. This then causes the 3331 to request DMA service, whereupon the DMA Controller reads or writes the selected Data Block from VME to the PC memory or vice–versa, starting from a pre–selected VME address. Only 16 bit data access is supported in this mode, since only one I/O address can be selected at a time.