The VXIbus communication standard encompasses device types, protocols, and communication handshakes.
Each VXIbus device in a VXIbus system is allocated one logical address, which can range from 0 to 255. Conversely, the VXIbus system can contain up to 256 logical devices. Note that although a VXI mainframe contains a maximum of 13 slots, each slot can contain multiple devices. A single device can also occupy more than one slot.
VXI devices have specific registers called configuration registers. These registers are located in the upper 16KB of the first 64KB. The logical address of a VXI device determines the location of the device’s configuration registers in the 16KB. Each device has its own 64 bytes of registers among which is the device configuration register.
The VXIbus standard includes four device types:
Register-based device
Message-based device
Extended device
Memory device
Register-based devices provide the basic level of communication to VXI devices. Communication is done through register reads and writes. VXI communication at the register-level is the simplest and least expensive to implement.
Message-based devices are more complex and intelligent and are capable of communicating with other message-based devices using ASCII data via the Word Serial Protocol. Although their ability to use ASCII communications makes message-based devices more versatile than register-based devices, they can also be slower and more expensive.
Memory devices provide the fastest access method by directly reading and writing to/from the VXI address space. These devices provide data storage in the form of blocks of ROM, RAM, etc. in the VXI address space.
Extended devices are VXI bus devices with provisions for defining new class of devices for future applications.
ATEasy supports all types of devices that use the VxiXXX functions. ATEasy supports message-based devices using its I/O Table mechanism.