Z80180 Datasheet, PDF (43/326 Pages) Zilog, Inc. – Z8018x Family MPU

Z 8018x Fam ily
M PU Us e r M anual
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externally synchronizing WAIT input transitions with the rising
edge of the system clock.
Dynamic RAM refresh is not performed during Wait States (TW) and
thus system designs which use the automatic refresh function must
consider the affects of the occurrence and duration of wait states (TW).
Figure 18 depicts WAIT timing.
T1 T2 TW TW T3
T1
Phi
WAIT
Figure 18. WAIT Timing Diagram
Programmable Wait State Insertion
In addition to the WAIT input, Wait States (TW) can also be inserted by
program using the Z8X180 on-chip Wait State generator (see Figure 19.
Wait State (TW) timing applies for both CPU execution and on-chip
DMAC cycles.
By programming the four significant bits of the DMA/Wait Control
Register (DCNTL) the number of Wait States, (TW) automatically
inserted in memory and I/O cycles, can be separately specified. Bits 4 and
5 specify the number of Wait States (TW) inserted for I/O access and bits
6 and 7 specify the number of Wait States (TW) inserted for memory
access. These bit pairs all 0–3 programmed Wait States for either I/O or
memory access.
UM005001-ZMP0400