ST & T UPSD3212C - Manual (Page 123)

123/163
uPSD3212A, uPSD3212C, uPSD3212CV
The PSD MODULE has a Turbo Bit in PMMR0.
This bit can be set to turn the Turbo Mode off (the
default is with Turbo Mode turned on). While Turbo
Mode is off, the PLDs can achieve standby current
when no PLD inputs are changing (zero DC cur-
rent). Even when inputs do change, significant
power can be saved at lower frequencies (AC cur-
rent), compared to when Turbo Mode is on. When
the Turbo Mode is on, there is a significant DC cur-
rent component and the AC component is higher.
Automatic Power-down (APD) Unit and Power-
down Mode. The APD Unit, shown in
Figure
65., page 122 , puts the PSD MODULE into Pow-
er-down Mode by monitoring the activity of Ad-
dress Strobe (ALE). If the APD Unit is enabled, as
soon as activity on Address Strobe (ALE) stops, a
four-bit counter starts counting. If Address Strobe
(ALE/AS, PD0) remains inactive for fifteen clock
periods of CLKIN (PD1), Power-down (PDN) goes
High, and the PSD MODULE enters Power-down
Mode, as discussed next.
Power-down Mode. By default, if you enable the
APD Unit, Power-down Mode is automatically en-
abled. The device enters Power-down Mode if Ad-
dress Strobe (ALE) remains inactive for fifteen
periods of CLKIN (PD1).
The following should be kept in mind when the
PSD MODULE is in Power-down Mode:
–
If Address Strobe (ALE) starts pulsing again,
the PSD MODULE returns to normal
Operating mode. The PSD MODULE also
returns to normal Operating mode if either
PSD Chip Select Input (CSI, PD2) is Low or
the RESET input is High.
– The MCU address/data bus is blocked from all
memory and PLDs.
– Various signals can be blocked (prior to
Power-down Mode) from entering the PLDs by
setting the appropriate bits in the PMMR
registers. The blocked signals include MCU
control signals and the common CLKIN (PD1).
Note: Blocking CLKIN (PD1) from the PLDs
does not block CLKIN (PD1) from the APD
Unit.
– All memories enter Standby Mode and are
drawing standby current. However, the PLD
and I/O ports blocks do
not go into Standby
Mode because you don’t want to have to wait
for the logic and I/O to “wake-up” before their
outputs can change. See Table
98 for Power-
down Mode effects on PSD MODULE ports.
– Typical standby current is of the order of
microamperes. These standby current values
assume that there are no transitions on any
PLD input.
Other Power Saving Options. The PSD MOD-
ULE offers other reduced power saving options
that are independent of the Power-down Mode.
Except for the SRAM Standby and PSD Chip Se-
lect Input (CSI, PD2) features, they are enabled by
setting bits in PMMR0 and PMMR2.
Figure 66. Enable Power-down Flow Chart
Table 98. Power-down Mode’s Effect on Ports
Port Function Pin Level
MCU I/O No Change
PLD Out No Change
Address Out Undefined
Peripheral I/O Tri-State
Enable APD
Set PMMR0 Bit 1 = 1
PSD Module in Power
Down Mode
ALE idle
for 15 CLKIN
clocks?
RESET
Yes
No
OPTIONAL
Disable desired inputs to PLD
by setting PMMR0 bits 4 and 5
and PMMR2 bits 2 through 6.
AI06609