Information Technology Reference
In-Depth Information
(d)
It defines valid data on the bus
22.5.9
What is the function of the
NDFD
handshaking line:
(a)
It defines that all the devices have received the data
(b)
It identifies when all the devices are ready
(c)
It resets the bus
(d)
It defines valid data on the bus
22.5.10
Define the operation of the handshaking lines on the IEEE-488 bus.
22.5.11
Define the actions of talkers, listeners and controllers on an IEEE-488 bus. Give
examples of each type of device.
22.5.12
The IEEE-488 bus is a common bus, where all the devices connect to each of the
signal lines. Why are most of the handshaking lines active low?
22.6 Notes from the author
This chapter has covered one of the most simple busses, the IEEE-488 bus, and one of the
most complex ones, the VME bus. So, why did I include them in a single chapter. Well, I
cheated a little, because they didn't really merit a chapter of their own, so I merged them
(I'm sure I'll receive lots of e-mails complaining about this, so I'll give them both a chapter
of their own in the second edition, if they both still exist and if I'm allowed a second edition).
The IEEE-488 is a beautifully designed bus, which is well supported by software ven-
dors, and is easy to set up. It will basically run quietly for many years without requiring any
intervention by the user. The connector and cable are very well designed and can stand a
great deal of abuse. It has typically been used a standard interface for instrumentation, but
the growth of the serial busses is likely to reduce its importance.
And what can I say about the VME bus. Oh boy, it's complex. Its little brother, the VXI is
a little less complex, but still is an extremely powerful and flexible bus for building modular
instrumentation systems. Unfortunately it suffers from being too flexible and can be complex
to write software for. The popularity of the PCI bus, and especially the CompactPCI bus (the
PCI bus for modular systems) is overtaking the VXI bus.
