
PSD4XX Famly
70
9.5.2   Oher Power Saving Options
The PSD4XX provides additional power saving options. These options, except the SRAM 
Standby Mode, can be enabled/disabled by setting up the corresponding bit in the PMMR.
J
 EPROM
The EPROM power consumption in the PSD is controlled by bit 3 in the 
PMMR0 – EPROM CMiser. Upon reset the CMiser bit is OFF. This will cause the 
EPROM to be ON at all times as long as CSI is enabled (low). The reason this mode is 
provided is to reduce the access time of the EPROM by 10 ns relative to the low power 
condition when CMiser is ON. If CSI is disabled (high) the EPROM will be deselected 
and will enter standby mode (OFF) overriding the state of the CMiser.
If CMiser is set (ON) then the EPROM will enter the standby mode when not selected. 
This condition can take place when CSI is high or when CSI is low and the EPROM is 
not accessed. For example, if the MCU is accessing the SRAM, the EPROM will be 
deselected and will be in low power mode.
An additional advantage of the CMiser is achieved when the PSD is configured in the 
by 8 mode (8 bit data bus). In this case an additional power savings is achieved in the 
EPROM (and also in the SRAM) by turning off 1/2 of the array even when the EPROM 
is accessed (the array is divided internally into odd and even arrays).
The power consumption for the different EPROM modes is given in the DC 
Characteristics table under I
CC
(DC) EPROM Adder.
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 SRAM Standby Mode
The SRAM has a dedicated supply voltage V
STBY
that can be used to connect a battery. 
When V
CC
becomes lower than V
STBY 
–0.6 then the PSD will automatically connect 
the V
STBY
as a power source to the SRAM. The SRAM Standby Current (I
STBY
) is 
typically 0.5 μA.
SRAM data retention voltage V
DF
is 2 V minimum.
J
 Zero Power ZPLD
ZPLD power/speed is controlled by the ZPLD_Turbo bit (bit 4) in the PMMR0. 
After reset the ZPLD is in Turbo mode and runs at full power and speed. By setting the 
bit to “1”, the Turbo mode is disabled and the ZPLD is consuming Zero Power current if 
the inputs are not switching for an extended time of 70 ns. The propagation delay time 
will be increased by 10ns after the Turbo bit is set to “1” (turned off) if the inputs change 
at a frequency of less than 15 MHz.
The PSD4XX
Architecture 
(cont.)