z80189 ZiLOG Semiconductor, z80189 Datasheet - Page 43

• Manufacturer Part Number: z80189
• Description: Z80180, Z8s180, Z8l180 Mpu Operation
• Manufacturer: ZiLOG Semiconductor

28
UM005003-0703
Z8018x
Family MPU User Manual
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.
Figure 18.
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.
WAIT
Phi
externally synchronizing WAIT input transitions with the rising
edge of the system clock.
WAIT Timing Diagram
T1
T2
TW
TW
T3
T1