MB81ES653225-12/-12L
15
7.
BANK SELECT (BA)
This SDR I/F FCRAM has two banks in one part and each bank is organized as 1 Mwords by 32-bit. Bank
selection by BA occurs at Bank Active command (ACTV) followed by read (READ or READA) , write (WRIT or
WRITA) , and precharge command (PRE) .
8.
DATA INPUT AND OUTPUT (DQ
31
to DQ
0
)
Input data is latched and written into the memory at the clock following the write command input. Data output is
obtained by the following conditions followed by a read command input :
t
RAC
; from the bank active command when t
RCD
(Min) is satisfied. (This parameter is reference only.)
t
CAC
; from the read command when t
RCD
is greater than t
RCD
(Min) . (This parameter is reference only.)
t
AC
; from the clock edge after t
RAC
and t
CAC
.
The polarity of the output data is identical to that of the input. Data is valid between access time (determined by
the three conditions above) and the next positive clock edge (t
OH
) .
9.
DATA I/O MASK (DQM)
DQM is an active high enable input and has an output disable and input mask function. During burst cycle and
when DQM
0
to DQM
3
=
High is latched by a clock, input is masked at the same clock and output will be masked
at the second clock later while internal burst counter will increment by one or will go to the next stage depending
on burst type. DQM
0
, DQM
1
, DQM
2
, DQM
3
, controls DQ
7
to DQ
0
, DQ
15
to DQ
8
, DQ
23
to DQ
16
, DQ
31
to DQ
24
,
respectively.
10. BURST MODE OPERATION AND BURST TYPE
The burst mode provides faster memory access. The burst mode is implemented by keeping the same row
address and by automatic strobing column address. Access time and cycle time of burst mode is specified as
t
AC
and t
CK
, respectively. The internal column address counter operation is determined by a mode register which
defines burst type and burst count length of 1, 2, 4 or 8 bits of boundary or full column. In order to terminate or
to move from the current burst mode to the next stage while the remaining burst count is more than 1, the following
combinations will be required.
The burst type can be selected either sequential or interleave mode if burst length is 2, 4 or 8. The sequential
mode is an incremental decoding scheme within a boundary address to be determined by count length, it assigns
+
1 to the previous (or initial) address until reaching the end of boundary address and then wraps round to least
significant address (
=
0) . The interleave mode is a scrambled decoding scheme for A
2
and A
0
. If the first access
of column address is even (0) , the next address will be odd (1) , or vice-versa. When the full column burst
operation is executed at single write mode, Auto-precharge command is valid only at write operation.
Current Stage
Next Stage
Method (Assert the following command)
Burst Read
Burst Read
Read Command
Burst Read
Burst Write
1st Step
Mask Command (Normally 3 clock cycles)
2nd Step
Write Command after l
OWD
Burst Write
Burst Write
Write Command
Burst Write
Burst Read
Read Command
Burst Read
Precharge
Precharge Command
Burst Write
Precharge
Precharge Command