Rev.0.9 / Dec.2000
21
Direct RDRAM
256/288-Mbit (512Kx16/18x32s) Preliminary
Write Transaction - Example
Figure 16: shows an example of a write transaction. It begins
by activating a bank with an ACT a0 command in an ROWA
packet. A time t
RCD
later a WR a1 command is issued in a
COLC packet. Note that the ACT command includes the
device, bank, and row address (abbreviated as a0) while the
WR command includes device, bank, and column address
(abbreviated as a1). A time t
CWD
after the WR command the
write data dualoct D(a1) is issued. Note that the packets on
the ROW and COL pins use the end of the packet as a timing
reference point, while the packets on the DQA/DQB pins
use the beginning of the packet as a timing reference point.
A time t
CC
after the first COLC packet on the COL pins a
second COLC packet is issued. It contains a WR a2
command. The a2 address has the same device and bank
address as the a1 address (and a0 address), but a different
column address. A time t
CWD
after the second WR
command a second write data dualoct D(a2) is issued.
A time t
RTR
after each WR command an optional COLM
packet MSK (a1) is issued, and at the same time a COLC
packet is issued causing the write buffer to automatically
retire. See Figure 17: for more detail on the write/retire
mechanism. If a COLM packet is not used, all data bytes are
unconditionally written. If the COLC packet which causes
the write buffer to retire is delayed, then the COLM packet
(if used) must also be delayed.
Next, a PRER a3 command is issued in an ROWR packet on
the ROW pins. This causes the bank to precharge so that a
different row may be activated in a subsequent transaction or
so that an adjacent bank may be activated. The a3 address
includes the same device and bank address as the a0, a1, and
a2 addresses. The PRER command must occur a time t
RAS
or more after the original ACT command (the activation
operation in any DRAM is destructive, and the contents of
the selected row must be restored from the two associated
sense amps of the bank during the t
RAS
interval).
A PRER a3 command is issued in an ROWR packet on the
ROW pins. The PRER command must occur a time t
RTP
or
more after the last COLC which causes an automatic retire.
Finally, an ACT b0 command is issued in an ROWR packet
on the ROW pins. The second ACT command must occur a
time t
RC
or more after the first ACT command and a time t
RP
or more after the PRER command. This ensures that the
bank and its associated sense amps are precharged. This
example assumes that the second transaction has the same
device and bank address as the first transaction, but a
different row address. Transaction b may not be started until
transaction a has finished. However, transactions to other
banks or other devices may be issued during transaction a.
Figure 16: Write Transaction Example
CTM/CFM
DQA8..0
DQB8..0
COL4
..COL0
ROW2
..ROW0
T
0
T
4
T
8
T
12
T
1
T
5
T
9
T
13
T
2
T
6
T
10
T
14
T
3
T
7
T
11
T
15
T
16
T
20
T
24
T
28
T
17
T
21
T
25
T
29
T
18
T
22
T
26
T
30
T
19
T
23
T
27
T
31
T
32
T
36
T
40
T
44
T
33
T
37
T
41
T
45
T
34
T
38
T
42
T
46
T
35
T
39
T
43
T
47
MSK (a2)
t
RTR
retire (a2)
MSK (a1)
retire (a1)
WR a1
PRER a3
WR a2
D (a2)
t
RCD
D (a1)
ACT b0
t
RC
t
RP
ACT a0
t
CWD
Transaction a: WR
Transaction b: xx
a0 = {Da,Ba,Ra}
b0 = {Da,Ba,Rb}
a1 = {Da,Ba,Ca1}
a2 = {Da,Ba,Ca2}
a3 = {Da,Ba}
t
CC
t
CWD
t
RTR
t
RAS
t
RTP