uPSD3234A, uPSD3234BV, uPSD3233B, uPSD3233BV
The PSD Module has a Turbo Bit in PMMR0. This
bit can be set to turn the Turbo Mode off (the de-
fault 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
puts the PSD Module into Power-
down Mode by monitoring the activity of Address
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
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 Module
offers other reduced power saving options that are
independent of the Power-down Mode. Except for
the SRAM Stand-by and PSD Chip Select Input
(CSI, PD2) features, they are enabled by setting
bits in PMMR0 and PMMR2.
Figure 70. Enable Power-down Flow Chart
RESET
–
Enable APD
Set PMMR0 Bit 1 = 1
OPTIONAL
Disable desired inputs to PLD
by setting PMMR0 bits 4 and 5
and PMMR2 bits 2 through 6.
No
ALE idle
for 15 CLKIN
clocks?
Yes
PSD Module in Power
Down Mode
AI06609
Table 101. Power-down Mode’s Effect on Ports
Port Function
MCU I/O
PLD Out
Address Out
Peripheral I/O
Pin Level
No Change
No Change
Undefined
Tri-State
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