Z80180 Datasheet, PDF (41/326 Pages) Zilog, Inc. – Z8018x Family MPU

Z 8018x Fam ily
M PU Us e r M anual
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When the bus is released, the address (A0–A19), data (D0–D7), and
control (MREQ, IORQ, RD, and WR) signals are placed in the high
impedance state.
Dynamic RAM refresh is not performed when the Z8X180 has released
the bus. The alternate bus master must provide dynamic memory
refreshing if the bus is released for long periods of time.
Figure 16 illustrates BUSREQ/BUSACK bus exchange during a memory
read cycle. Figure 17 illustrates bus exchange when the bus release is
requested during a Z8X180 CPU internal operation. BUSREQ is sampled
at the falling edge of the system clock prior to T3, T1 and Tx (BUS
RELEASE state). If BUSREQ is asserted Low at the falling edge of the
clock state prior to Tx, another Tx is executed.
CPU memory read cycle
Bus release cycle
CPU cycle
T1 T2 TW T3 TX TX T1 T1
Phi
A0–A19
D0–D7
MREQ
IORQ
RD, WR
BUSREQ
BUSACK
Figure 16. Bus Exchange Timing During Memory Read
UM005001-ZMP0400