W988D6FB_13 Datasheet, PDF (24/66 Pages) Winbond – 256Mb Mobile LPSDR

W988D6FB / W988D2FB
256Mb Mobile LPSDR
9.3 Precharge
There are two commands which perform the Precharge operation: Bank Precharge and Precharge All. When the Bank Precharge
command is issued to the active bank, the bank is precharged and then switched to the idle state. The Bank Precharge command
can precharge one bank independently of the other bank and hold the unprecharged bank in the active state. The maximum time
each bank can be held in the active state is specified as t_RAS (max). Therefore, each bank must be precharged within t_RAS (max)
from the Bank Activate command.
The Precharge All command can be used to precharge all banks simultaneously. Even if banks are not in the active state, the
Precharge All command can still be issued. In this case, the Precharge operation is performed only for the active bank and the
precharged bank is then switched to the idle state.
9.3.1 Auto Precharge
Auto precharge is a feature that performs the same individual-bank PRECHARGE function described previously, without requiring
an explicit command. This is accomplished by using A10 to enable auto precharge in conjunction with a specific READ or WRITE
command. A precharge of the bank/row that is addressed with the READ or WRITE command is automatically performed upon
completion of the READ or WRITE burst.
Auto precharge ensures that the precharge is initiated at the earliest valid stage within a burst. Another command cannot be issued
to the same bank until the precharge time (tRP) is completed. This is determined as if an explicit PRECHARGE command was
issued at the earliest possible time.
Winbond SDRAM supports concurrent auto precharge; cases of concurrent auto precharge for READs and WRITEs are defined
below.
9.3.2 READ with auto precharge interrupted by a READ (with or without auto precharge)
A READ to bank m will interrupt a READ on bank n following the programmed CAS latency. The precharge to bank n
begins when the READ to bank m is registered.
T0
T1
T2
T3
T4
T5
T6
T7
CLK
Command
NOP
READ-AP
Bank n
NOP
READ-AP
Bank m
NOP
NOP
Internal
states
Bank n
Bank m
Page active
READ with burst of 4
Page active
Interrupt burst, precharge
tRP-bank n
READ with burst of 4
NOP
NOP
Idle
tRP-bank m
Precharge
Address
DQ
Bank n,
Col a
Bank m,
Col d
CL=3 (bank n)
Dout
a
Dout
a+1
CL=3 (bank m)
Note: 1. DQM is LOW.
Dout
d
Dout
d+1
Don’t Care
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Publication Release Date : August 15, 2013
Revision A01-004