Commodore Amiga A500 Technical Reference Manual page 22

GLOSSARY
Active Active high signals are considered active when they are in
the "one state" or "high state". Active low signals are considered ac-
tive when they are "low" or in the "zero state". Active high signals
do not have barred signal names. Active low signals do have barred
signal names. Active means that the signal is
1. is true (non-barred) and is currently in the one state, or
2. is a barred signal name and is currently in the zero state.
An example is AS* (the * = bar). AS* is active when it is equal to
zero. A counter example is the signal AS (the inverse of AS*), which
is active when it is in the one state.
Auto Configuration The protocol (specified in this section) that
Amiga uses to configure expansion cards into the system.
Downstream Downstream means closer to the Amiga. For in-
stance, if two backplanes are daisy chained on the bus, the closer-in
backplane is downstream from the further-out backplane. The con-
cepts of upstream and downstream are important in determining
which direction the address and data drivers should drive.
Master A PIC which is capable of initiating DMA cycles on the bus.
PIC A PIC is a plug-in card or a product which behaves in the system
as a plug-in card. That is, it provides a resource that resides on the
expansion bus, and follows the rules for auto-config, master pro-
tocol, slave protocol, etc.
Slave A slave is a PIC that can only respond to bus cycles. A slave
cannot initiate bus cycles: in other words, it does not drive the ad-
dress lines on the backplane, nor AS*, UDS*, LDS*.
Upstream Upstream means further away from the processor. For
instance, all PICs are upstream from the buffers on the backplane
that they are plugged into because the buffers are between the PIC
and the Amiga.
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