Z85230 Datasheet, PDF (111/120 Pages) Zilog, Inc. – ENHANCED SERIAL COMMUNICATIONS CONTROLLER

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In this mode, the Anti-Lock feature is not enabled. The FIFO is locked after the last
character of a frame has been transferred, and the interrupt condition does not
disappear until after an Error Reset command is issued to the ESCC. No Reset
Highest IUS command can clear any IP bit.
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If both conditions are satisfied, allowing nested interrupts can solve the problem.
The processor servicing an interrupt on the daisy chain must be interruptible again
from another interrupt of higher priority on that same daisy chain.
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