Data Sheet
March 2000
DSP1627 Digital Signal Processor
Lucent Technologies Inc.
29
4 Hardware Architecture
(continued)
4.13 Power Management
There are three different control mechanisms for putting
the DSP1627 into low-power modes: the powerc control
register, the STOP pin, and the AWAIT bit in the alf reg-
ister. The PLL can also be disabled with the PLLEN bit
of the pllc register for more power saving.
Powerc Control Register Bits
The powerc register has 10 bits that power down vari-
ous portions of the chip and select the clock source:
XTLOFF:
Assertion of the XTLOFF bit powers down the
crystal oscillator or the small-signal input circuit, dis-
abling the internal processor clock. Assertion of the
XTLOFF bit to disable the crystal oscillator also pre-
vents its use as a noninverting buffer. Since the oscilla-
tor and the small-signal input circuits take many cycles
to stabilize, care must be taken with the turn-on se-
quence, as described later.
SLOWCKI:
Assertion of the SLOWCKI bit selects the
ring oscillator as the clock source for the internal pro-
cessor clock instead of CKI or the PLL. When CKI or the
PLL is selected, the ring oscillator is powered down.
Switching of the clocks is synchronized so that no par-
tial or short clock pulses occur. Two
nop
s should follow
the instruction that sets or clears SLOWCKI.
NOCK:
Assertion of the NOCK bit synchronously turns
off the internal processor clock, regardless of whether
its source is provided by CKI, the PLL, or the ring oscil-
lator. The NOCK bit can be cleared by resetting the chip
with the RSTB pin, or asserting the INT0 or INT1 pins.
Two
nop
s should follow the instruction that sets NOCK.
The PLL remains running, if enabled, while NOCK is
set.
INT0EN:
This bit allows the INT0 pin to asynchronously
clear the NOCK bit, thereby allowing the device to con-
tinue program execution from where it left off without
any loss of state. No chip reset is required. It is recom-
mended that, when INT0EN is to be used, the INT0
interrupt be disabled in the inc register so that an unin-
tended interrupt does not occur. After the program re-
sumes, the INT0 interrupt in the ins register should be
cleared.
INT1EN:
This bit enables the INT1 pin to be used as the
NOCK clear, exactly like INT0EN previously described.
The following control bits power down the peripheral
I/O units of the DSP. These bits can be used to further
reduce the power consumption during standard sleep
mode.
SIO1DIS:
This is a powerdown signal to the SIO1 I/O
unit. It disables the clock input to the unit, thus eliminat-
ing any sleep power associated with the SIO1. Since
the gating of the clocks may result in incomplete trans-
actions, it is recommended that this option be used in
applications where the SIO1 is not used or when reset
may be used to reenable the SIO1 unit. Otherwise, the
first transaction after reenabling the unit may be corrupt-
ed.
SIO2DIS:
This bit powers down the SIO2 in the same
way SIO1DIS powers down the SIO1.
PHIFDIS:
This is a powerdown signal to the parallel
host interface. It disables the clock input to the unit, thus
eliminating any sleep power associated with the PHIF.
Since the gating of the clocks may result in incomplete
transactions, it is recommended that this option be used
in applications where the PHIF is not used, or when re-
set may be used to reenable the PHIF. Otherwise, the
first transaction after reenabling the unit may be corrupt-
ed.
TIMERDIS:
This is a timer disable signal which disables
the clock input to the timer unit. Its function is identical
to the DISABLE field of the timerc control register. Writ-
ing a 0 to the TIMERDIS field will continue the timer op-
eration.
Figure 7 shows a functional view of the effect of the bits
of the powerc register on the clock circuitry. It shows
only the high-level operation of each bit. Not shown are
the bits that power down the peripheral units.
STOP Pin
Assertion (active-low) of the STOP pin has the same ef-
fect as setting the NOCK bit in the powerc register. The
internal processor clock is synchronously disabled until
the STOP pin is returned high. Once the STOP pin is re-
turned high, program execution will continue from
where it left off without any loss of state. No chip reset
is required. The PLL remains running, if enabled, during
STOP assertion.
The pllc Register Bits
The PLLEN bit of the pllc register can be used to power
down the clock synthesizer circuitry. Before shutting
down the clock synthesizer circuitry, the system clock
should be switched to either CKI using the PLLSEL bit
of pllc, or to the ring oscillator using the SLOWCKI bit of
powerc.