Zilog Z16C35 User Manual
Page 190
Application Note
The Z180™ Interfaced with the SCC at MHZ
7
The SCC uses /INTACK (Interrupt Acknowledge) for
recognition of an interrupt acknowledge cycle. This pin,
used with /RD, allows the SCC to gate its interrupt vector
onto the data bus. An active /RD signal during an interrupt
acknowledge cycle performs two functions. First, it allows
the highest priority device requesting an interrupt to place
its vector on the data bus. Secondly, it sets the IUS bit in
the highest priority device to show the device is now under
service.
Figure 12. SCC Interrupt Status Diagram
IP
Set
INT
Active
IUS
Set
IP
Cleared
IUS
Cleared
Interrupt Condition
Return To Main Program
CPU Read, Write, or Reset
IEO High?
IEI High?
/INTACK * IEI * /RD
Wait For CPU
/INTACK Cycle
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