Z8S18020FSC Datasheet, PDF (62/70 Pages) Zilog, Inc. – ENHANCED Z180 MICROPROCESSOR

Z80180/Z8S180/Z8L180
Enhanced Z180 Microprocessor
Zilog
Table 14. DRAM Refresh Intervals
CYC1 CYC0
0
0
0
1
1
0
1
1
Note: *calculated interval
Insertion
Interval
10 states
20 states
40 states
80 states
Ø: 10 MHz
(1.0 µs)*
(2.0 µs)*
(4.0 µs)*
(8.0 µs)*
8 MHz
(1.25 µs)*
(2.5 µs)*
(5.0 µs)*
(10.0 µs)*
Time Interval
6 MHz
1.66 µs
3.3 µs
6.6 µs
13.3 µs
4 MHz
2.5 µs
5.0 µs
10.0 µs
20.0 µs
2.5 MHz
4.0 µs
8.0 µs
16.0 µs
32.0 µs
Refresh Control and Reset. After RESET, based on the
initialized value of RCR, refresh cycles will occur with an
interval of 10 clock cycles and be 3 clock cycles in dura-
tion.
Dynamic RAM Refresh Operation
1. Refresh Cycle insertion is stopped when the CPU is in
the following states:
a. During RESET
b. When the bus is released in response to
BUSREQ.
c. During SLEEP mode.
d. During WAIT states.
2. Refresh cycles are suppressed when the bus is
released in response to BUSREQ. However, the
refresh timer continues to operate. Thus, the time at
which the first refresh cycle occurs after the
Z80180/Z8S180/Z8L180 re-acquires the bus depends
on the refresh timer and has no timing relationship with
the bus exchange.
3. Refresh cycles are suppressed during SLEEP mode.
If a refresh cycle is requested during SLEEP mode,
the refresh cycle request is internally “latched” (until
replaced with the next refresh request). The “latched”
refresh cycle is inserted at the end of the first machine
cycle after SLEEP mode is exited. After this initial
cycle, the time at which the next refresh cycle occurs
depends on the refresh time and has no relationship
with the exit from SLEEP mode.
4. The refresh address is incremented by one for each
successful refresh cycle, not for each refresh. Thus,
independent of the number of “missed” refresh
requests, each refresh bus cycle will use a refresh
address incremented by one from that of the previous
refresh bus cycles.
MMU COMMON BASE REGISTER
Mnemonic CBR
Address 38
MMU Common Base Register (CBR). CBR specifies the
base address (on 4 KB boundaries) used to generate a 20-
bit physical address for Common Area 1 accesses. All bits
of CBR are reset to 0 during RESET.
7
Bit
CB7
R/W
6
CB6
R/W
5
CB5
R/W
4
CB4
R/W
3
CB3
R/W
2
CB2
R/W
1
CB1
R/W
0
CB0
R/W
Figure 79. MMU Common Base Register (BBR: I/O Address = 38H)
1-62
PRELIMINARY
DS971800401