Z380 Datasheet, PDF (97/115 Pages) Zilog, Inc. – MICROPROCESSOR

ZILOG
LOW POWER STANDBY MODE
MICROPROCESSOR
The Z380 MPU provides an optional standby mode to
minimize power consumption during system idle time. If
this option is enabled, executing the Sleep instruction
would stop clocking internal to the Z380 MPU, as well as at
the BUSCLK and IOCLK outputs. The /STNBY signal goes
to active logic 0, indicating the Z380 MPU is entering the
standby mode. All Z380 MPU operations are suspended,
the bus control signals are driven inactive and the address
bus is driven to logic 1s. Note that if an external crystal
oscillator is used to drive the Z380 MPU’s CLKI input,
/STNBY can be used to stop its operation. This is a means
to further reduce power dissipation for the overall system.
The standby mode can be exited by asserting any of the
/RESET, /NMI, /INT3-/INT0 (if enabled), or optionally,
/BREQ inputs.
If the standby mode option is not enabled, the Sleep
instruction is interpreted and executed no different than
the HALT instruction, stopping the Z30 MPU from further
instruction execution. In this case, /HALT goes to active
logic 0 to indicate the Z380 MPU's halt status.
Standby Mode Control and Entering
STBY (Enable Standby Mode Option). Enables the Z380
MPU to go into low power standby mode when the Sleep
instruction is executed.
BRXT (Bus Request to Exit Standby Mode). If BRXT is at
logic 1, standby mode can be exited by asserting /BREQ.
Reserved Bits 5-3. Read as 0s, should write to as 0s.
WM2-WM0 (Warm-up Time Selection). WM2-WM0 deter-
mines the approximate running duration of a warm-up
counter that provides a delay before the Z380 MPU
resumes its clocking and operations, from the time an
interrupt or bus request (if so enabled) is asserted to exit
standby mode. In a system where an external crystal
oscillator is used to drive the Z380 MPU’s CLK input, an
appropriate warm-up time can be selected for the oscilla-
tor to stabilize.
SMCR: 00000016H
R/W
7
0
STBY BRXT
WM2 WM1 WM0
0
0
0
0
0
0
0
0 Reset Value
Warmup Time Selection
000
001
010
No Warmup
2 ¹⁶ BUSCLK Cycles
2 ¹⁷ BUSCLK Cycles
100
2 ¹⁹ BUSCLK Cycles
Reserved
Program as 0s
Read as 0s
Bus Request to Exit Standby Mode
Enable Standby Mode Option
Figure 51. Standby Mode Control Register
PS010001-0301