Glossary-1
GLOSSARY
This glossary defines acronyms, abbreviations, and terms that have special meaning in this m an-
ual. (Chapter 1, GUIDE TO THIS MANUAL, discusses notational conventions.)
Assert The act of making a signal active (enabled). The
polarity (high/low) is defined by the signal name.
Active-low signals are designated by a pound symbol
(#) suffix; active-high signals have no suffix. To
assert RD# is to drive it low; to assert HLDA is to
drive it high.
BIOS Basic input/output system. The interface between the
hardware and the operating system.
BIU Bus interface unit. The internal peripheral that
controls the external bus.
Boundary-scan The term boundary-scan refers to the ability to scan
(observe) the signals at the boundary (the pins) of a
device. A major component of the JTAG standard.
CSU Chip-select unit. The internal peripheral that selects
an external memory device during an external bus
cycle.
Clear The term clear refers to the value of a bit or the act of
giving it a value. If a bit is clear, its value is “0”;
clearing a bit gives it a “0” value.
Deassert The act of making a signal inactive (disabled). The
polarity (high/low) is defined by the signal name.
Active-low signals are designated by a pound symbol
(#) suffix; active-high signals have no suffix. To
deassert RD# is to drive it high; to deassert HLDA i s
to drive it low.
DMA Direct memory access controller. The internal
peripheral that allows external or internal peripherals
to transfer information directly to or from the system.
The two-channel DMA controller is an enhanced
version of the industry-standard 8237A DMA
peripheral.
DOS Address Space Addresses 0H–03FFH. The internal timers, interrupt
controller, serial I/O ports, and DMA controller can