z80180 ZiLOG Semiconductor, z80180 Datasheet - Page 76

• Manufacturer Part Number: z80180
• Description: Microprocessor Unit
• Manufacturer: ZiLOG Semiconductor

Table 19. DRAM Refresh Intervals
PS014004-1106
CYC1 CYC0
0
0
1
1
*Calculated interval.
0
1
0
1
CYC1, 0: Cycle Interval (bit 1,0)—
cycles) between refresh cycles. In the case of dynamic RAMs requiring 128 refresh cycles
every 2 ms (or 256 cycles in every 4 ms), the required refresh interval is less than or equal to
15.625 µs. The underlined values indicate the best refresh interval depending on CPU clock
frequency.
Insertion Interval
10 states
20 states
40 states
80 states
Refresh Control and RESET
After
10 clock cycles and be 3 clock cycles in duration.
Dynamic RAM Refresh Operation
1.
2. Refresh cycles are suppressed when the bus is released in response to
3. Refresh cycles are suppressed during
REFRESH CYCLE
However, the refresh timer continues to operate. The time at which the first refresh cycle
occurs after the Z80180 reacquires the bus depends on the refresh timer, and possesses
no timing relationship with the bus exchange.
SLEEP
refresh request). The latched refresh cycle is inserted at the end of the first machine
cycle after
refresh cycle occurs depends on the refresh time and carries no relationship with the exit
from
RESET
SLEEP
CYC0
mode, the refresh cycle request is internally latched (until replaced with the next
a. During
b. When the bus is released in response to
c. During
d. During
, based on the initialized value of
SLEEP
mode.
and
Time Interval
Ø: 10 MHz
(1.0 µs)*
(2.0 µs)*
(4.0 µs)*
(8.0 µs)*
CYC1
mode is exited. After this initial cycle, the time at which the next
insertion is stopped when the CPU is in the following states:
RESET
SLEEP
WAIT
are cleared to
states
mode
8 MHz
(1.25 µs)* 1.66 µs 2.5 µs
(2.5 µs)*
(5.0 µs)*
(10.0 µs)* 13.3 µs 20.0 µs 32.0 µs
CYC1
SLEEP
0
during
6 MHz
3.3 µs
6.6 µs
and
RCR
mode. If a refresh cycle is requested during
CYC0
, refresh cycles occur with an interval of
RESET
4 MHz
5.0 µs
10.0 µs 16.0 µs
specify the interval (in clock
BUSREQ
(see
Table
2.5 MHz
4.0 µs
8.0 µs
Microprocessor Unit
19).
BUSREQ
Architecture
.
Z80180
70