Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 221)

Detailed Flowcharts
Appendix D
DĆ17
Figure D.20
POWERUP Subroutine
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POWERUP
SPAWN RCVE
SPAWN XMIT
Continue
Initialization
POWERUP
At power-up the Z-80
starts executing code at
Location 0. The POWERUP
routine starts the XMIT and
RCVE processes by executing
a SPAWN. A SPAWN is very
similar to a WAKEUP, except
the corresponding SLEEP is
imaginary and is located ahead
of the first instruction of the
SPAWNed process.
Figure D.21
Message Queue
FIRST
LAST
NEXT
MESSAGE
SIZE
STATUS
Network
Data
Block
NEXT
MESSAGE
SIZE
STATUS
Network
Data
Block
0
MESSAGE
SIZE
STATUS
Network
Data
Block
ROOT
MESSAGE
CONTROL BLOCKS
MESSAGES
The address of a
queue is the
address of its root.
NOTE: Messages are added to the
end of the queue and removed from
the head.
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