
September 15, 2005 S71WS-N_01_A4
S71WS-Nx0 Based MCPs
157
A d v a n c e I n f o r m a t i o n
42 Low Power Features
42.1
Internal TCSR
The internal Temperature Compensated Self Refresh (TCSR) feature is a very useful tool for re-
ducing standby current at room temperature (below 40°C). DRAM cells have weak refresh
characteristics in higher temperatures. High temperatures require more refresh cycles, which can
lead to standby current increase.
Without the internal TCSR, the refresh cycle should be set at worst condition so as to cover the
high temperature (85°C) refresh characteristics. But with internal TCSR, a refresh cycle below
40°C can be optimized, so the standby current at room temperature can be greatly reduced. This
feature is beneficial since most mobile phones are used at or below 40°C in the phone standby
mode.
Figure 42.1 PAR Mode Execution and Exit
Table 42.1 PAR Mode Characteristics
Notes:
1.
2.
Only the data in the refreshed block are valid.
The PAR Array can be selected through Mode Register Set (see
Mode Register Setting Operation
).
42.2
Driver Strength Optimization
The optimization of output driver strength is possible through the mode register setting to adjust
for the different data loadings. Through this driver strength optimization, the device can minimize
the noise generated on the data bus during read operation. The device supports full drive, 1/2
drive and 1/4 drive.
42.3
Partial Array Refresh (PAR) mode
The PAR mode enables the user to specify the active memory array size. The pSRAM consists of
4 blocks and the user can select 1 block, 2 blocks, 3 blocks or all blocks as active memory arrays
through the Mode Register Setting. The active memory array is periodically refreshed whereas
the disabled array is not refreshed, so the previously stored data is lost. Even though PAR mode
is enabled through the Mode Register Setting, PAR mode execution by the MRS# pin is still
needed. The normal operation can be executed even in refresh-disabled array as long as the
MRS# pin is not driven to the Low condition for over 0.5μs. Driving the MRS# pin to the High
condition puts the device back to the normal operation mode from the PAR executed mode. Refer
to
Figure 42.1
and
Table 42.1
for PAR operation and PAR address mapping.
Power Mode
Address
(Bottom Array)
(note 2)
000000h
–
7FFFFFh
000000h
–
5FFFFFh
000000h
–
3FFFFFh
000000h
–
1FFFFFh
Address
(Top Array)
(note 2)
000000h
–
7FFFFFh
200000h
–
7FFFFFh
400000h
–
7FFFFFh
600000h
–
7FFFFFh
Memory Cell
Data
Standby Current
(μA, Max)
Wait Time
(μs)
Standby (Full Array)
Partial Refresh(3/4 Block)
Partial Refresh(1/2 Block)
Partial Refresh(1/4 Block)
Valid (note 1)
200
170
150
140
0
MRS#
MODE
CS#
Normal
Operation
0.5
μ
s
Suspend
PAR mode
Normal
Operation