Z85233 Datasheet, PDF (198/317 Pages) Zilog, Inc. – The Zilog SCC Serial Communication Controller

Application Note
The Zilog Datacom Family with the 80186 CPU
RAM Size
32K x 8
128K x 8
Table 6. Address Ranges for Reset
MMCS value
3BFF
DBFF
Address Range for which ISCC,
IUSC, and (M)USC are Reset:
8
3B000-3B7FF
DB000-DB7FF
The three LSBs of the above MMCS values are 111 so that
the longest possible Reset pulse is generated when any of
the locations in the indicated range are accessed.
Interrupt Daisy Chain (Priority) Order
Jumper block J25 selects whether the (E)SCC device is at
the start or the end of the interrupt daisy chain.
Note that if this feature is not needed, it can be disabled by
simply not programming the MMCS register.
To make the interrupt priority be:
(E)SCC highest, IUSC, ISCC, (M)USC lowest
IUSC highest, ISCC, MUSC, (E)SCC lowest
IUSC highest, ISCC, USC, (E)SCC lowest
This variability is provided in part because early versions
of the 85230 ESCC had trouble passing an interrupt
acknowledge down the daisy chain if it occurred in
Jumper J25 as follows:
J25-J2 to J25-J3, J25-J4 to J25-J5 (J25-J1, J25X open)
J25-J1 to J25-J2, J25-J to J25-J4 (J25-5J, J25X open)
J25X to J25-J2, J25-J3 to J25-J4 (J25-J1, J25-J5 open)
response to a lower-priority device’s request just as the
ESCC was starting to make its own request. Current
85230’s don’t have the problem.
UM010901-0601
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