Filter
Top Products
© National Instruments Corporation 6-1 VXI-MXI User Manual
Chapter 6
Theory of Operation
A brief description of the VXI-MXI is given in Chapter 2 along with a functional block diagram
(see Figure 2-1). The major elements of the VXI-MXI are discussed in more detail in this
chapter. For a detailed discussion of the VXIbus, refer to the VXIbus specification and the
VMEbus specification. For a description of MXIbus, refer to the MXIbus specification.
VMEbus Address and Address Modifier Transceivers
The VMEbus address transceivers and associated logic control the direction of the VMEbus
address lines and latch incoming address lines on the assertion edge of the VMEbus Address
Strobe signal. The VMEbus Address Modifier lines are also controlled by this circuitry and are
also latched on the assertion edge of the address strobe.
VXIbus System Controller Functions
If the VXI-MXI is configured as the VMEbus System Controller, this circuitry provides the
16 MHz VMEbus system clock and the VMEbus data transfer bus arbiter. It also sources the
CLK10 signal and provides a MODID register, as required for a VXIbus Slot 0 device.
The 16 MHz system clock driver is derived from an onboard clock with an accuracy of 100 ppm
and a duty cycle of 50% (± 5%). The data transfer bus arbiter capability (PRI ARBITER)
accepts bus requests from all four VMEbus requester levels, prioritizes the requests, and grants
the bus to the highest priority requester.
The VXIbus specification requires Slot 0 devices to generate the VXIbus CLK10 signal on a
differential ECL output. The VXI-MXI has the option to source this CLK10 signal with either
an onboard 10 MHz clock with a 50% duty cycle or an external frequency source connected to
the EXT CLK SMB connector on the front panel. The MODID register required for Slot 0
devices is used to control and monitor the MODID lines. In accordance with the VXIbus
specification for a Slot 0 device, the VXI-MXI pulls up each MODID line with a 16.9 k
resistor. When the VXI-MXI is not a Slot 0 device, the MODID0 line is pulled to ground with a
825 resistor.
VMEbus Data Transceivers
The VMEbus data transceivers control the sending and receiving of data on the 32-bit data bus
from the VMEbus.