Rana Systems Elite Series - Manual (Page 174)

ELITE SERIES USER MANUAL THEORY OF OPERATION
code to map out all other controllers’ ROMs
without affecting itself.
This mapping of the 2K peripheral RCA space
($C800-$CFFF) is a convention maintained by
nearly all of the hardware and software develop-
ers.
The partitioning of the EPROM is performed by
u16 (7418257) and selection of the expansion
portion is done by U7 (74L574) and U16
(74LS257). Decoding of the off instruction is
performed by U15 (74LS30). A synchronous ap-
proach was taken to selection design because of
noise spikes on many of the bus interface lines.
7 . 2 . 5 . S t a t e M a c h i n e
This consists of a program counter latch, a
control latch, and a condition matrix contained
in a 256/512 byte PROM. The present program
counter address (which is completely independent
from the 6502 central processor ‘s program count-
er) and the condition lines are the inputs to
the condition matrix PROM.
Separate state diagrams exist for every kind of
activity allowed by the controller. These
states are selected by two of the condition
lines.
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