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7-3
REFRESH CONTROL UNIT
Figure 7-2. Refresh Control Unit Operation Flow Chart
The nine-bit refresh clock counter does not wait until the BIU services the refresh request to con-
tinue counting. This operation ensures that refresh requests occur at the correct interval. Other-
wise, the time between refresh requests would be a function of varying bus activity. When the
BIU services the refresh request, it clears the request and increments the refresh address.
Counter = ?
Load Counter
From Refresh Clock
Interval Register
Set "E" Bit
Refresh Control
Unit Operation
Decrement
Counter
Generated BIU
Request
Refresh Request
Acknowledged
BIU Refresh
Bus Operation
Execute
Memory Read
Executed
Every
Clock
Remove
Request
Continue
Increment
Address
A1265-0A