z80189 ZiLOG Semiconductor, z80189 Datasheet - Page 53

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

38
UM005003-0703
Z8018x
Family MPU User Manual
STANDBY Mode Exit with BUS REQUEST
1. Set bits 6 and 3 to
2. Set the I/O STOP bits (bit 5 of ICR, I/O Address =
3. Execute the SLEEP instruction.
When the device is in STANDBY mode, it performs similar to the
SYSTEM STOP mode as it exists on the Z80180-class processors, except
that the STANDBY mode stops the external oscillator, internal clocks and
reduces power consumption to 50 mA (typical).
Because the clock oscillator has been stopped, a restart of the oscillator
requires a period of time for stabilization. An 18-bit counter has been
added in the Z8S180Z8L180 to allow for oscillator stabilization. When
the part receives an external IRQ or BUSREQ during STANDBY mode,
the oscillator is restarted and the timer counts down 2
acknowledgment is sent to the interrupt source.
The recovery source must remain asserted for the duration of the 2
count, otherwise STANDBY restarts.
Optionally, if the BREXT bit (D5 of CPU Control Register) is set to 1, the
Z8S180 exits STANDBY mode when the BUSREQ input is asserted. The
crystal oscillator is then restarted. An internal counter automatically
provides time for the oscillator to stabilize, before the internal clocking
and the system clock output of the Z8S180 are resumed.
The Z8S180 relinquishes the system bus after the clocking is resumed by:
•
•
•
The Z8S180 regains the system bus when BUSREQ is deactivated. The
address outputs and the bus control outputs are then driven High. The
STANDBY mode is exited.
3-State the address outputs A19–A0
3-State the bus control outputs MREQ, IORQ, RD, and WR
Asserting BUSACK
1
and
0
, respectively.
17
3FH
counts before
) to
1
.
17