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Appendix B -
State Sequencing
COSMAC STATES/CYCLES
STATE CODES
SO
INSTRUCTION FETCH CYCLE
CYCLE TYPE
S1
INSTRUCTION EXECUTE CYCLE
S1 I
~
6 (I/O INSTR.)
S2
DMA BYTE TRANSFER CYCLE
S2 CYCLE (DMA I/O)
S3
INTERRUPT CYCLE
S3 CYCLE (INTERRUPT)
OTHER CYCLES
COSMAC STATE TRANSITION DIAGRAM
92C5-26537
START UP & NORMAL INSTRUCTION SEQUENCE:
EXTERNAL
-+
CLEAR
INTERNAL
-->
S1
STATE CODE
-->
HH
EFFECT OF DMA IN/DMA OUT/INTERRUPT ON NORMAL SEQUENCE
I
EXTERNAL
-+
I ...
INTERNAL
-+
STATE CODE-+
SCI
SCO
H
L
L
H
L
L
H
'H
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