EDR2518ABSE
4. DQ Packet Timing
Figure 4-1 shows the timing relationship of COLC packets with D and Q data packets. This document uses a
specific convention for measuring time intervals between packets: all packets on the ROW and COL pins (ROWA,
ROWR, COLC, COLM, COLX) use the trailing edge of the packet as a reference point, and all packets on the
DQA/DQB pins (D and Q) use the leading edge of the packet as a reference point.
An RD or RDA command will transmit a dualoct of read data Q a time tCAC later. This time includes one to five
cycles of round-trip propagation delay on the Channel. The tCAC parameter may be programmed to a one of a range
of values (8, 9, 10, 11, or 12 tCYCLE). The value chosen depends upon the number of RDRAM devices on the Channel
and the RDRAM device timing bin. See Figure 22-1(5/7) “TPARM Register” for more information.
A WR or WRA command will receive a dualoct of write data D a time tCWD later. This time does not need to include
the round-trip propagation time of the Channel since the COLC and D packets are traveling in the same direction.
When a Q packet follows a D packet (shown in the left half of the figure), a gap (tCAC-tCWD) will automatically appear
between them because the tCWD value is always less than the tCAC value. There will be no gap between the two COLC
packets with the WR and RD commands which schedule the D and Q packets.
When a D packet follows a Q packet (shown in the right half of the figure), no gap is needed between them because
the tCWD value is less than the tCAC value. However, a gap of tCAC - tCWD or greater must be inserted between the
COLC packets with the RD WR commands by the controller so the Q and D packets do not overlap.
Figure 4-1 Read (Q) and Write (D) Data Packet - Timing for tCAC = 8,9,10,11 or 12 tCYCLE
T
T
T
T
T
T
T
T
T
T
T
T
11T
T
T
T
15 T
T
T
T
19 T
T
T
T
23 T
T
T
T
27T
T
T
T
31 T
T
T
T
35 T
T
T
T
39 T
T
T
T
43T
T T T
45 46 47
44
1
2
3
5
6
7
9
10
13 14
17 18
21 22
25 26
29 30
33 34
37 38
41 42
0
4
8
12
16
20
24
28
32
36
40
CTM/CFM
This gap on the DQA/DQB pins appears automatically
This gap on the COL pins must be inserted by the controller
ROW2
..ROW0
tCAC -tCWD
tCAC -tCWD
WR d1
•••
tCWD
•••
tCWD
COL4
WR a1
RD b1
RD c1
..COL0
Q (c1)
D (d1)
Q (b1)
D (a1)
DQA8..0
DQB8..0
tCAC
•••
•••
tCAC
5. COLM Packet to D Packet Mapping
Figure 5-1 shows a write operation initiated by a WR command in a COLC packet. If a subset of the 16 bytes of
write data are to be written, then a COLM packet is transmitted on the COL pins a time tRTR after the COLC packet
containing the WR command. The M bit of the COLM packet is set to indicate that it contains the MA and MB mask
fields. Note that this COLM packet is aligned with the COLC packet which causes the write buffer to be retired. See
Figure 15-1 for more details.
If all 16 bytes of the D data packet are to be written, then no further control information is required. The packet slot
that would have been used by the COLM packet (tRTR after the COLC packet) is available to be used as an COLX
packet. This could be used for a PREX precharge command or for a housekeeping command (this case is not
shown). The M bit is not asserted in an COLX packet and causes all 16 bytes of the previous WR to be written
unconditionally. Note that a RD command will never need a COLM packet, and will always be able to use the COLX
packet option (a read operation has no need for the byte-write-enable control bits).
The figure 5-1 also shows the mapping between the MA and MB fields of the COLM packet and bytes of the D
packet on the DQA and DQB pins. Each mask bit controls whether a byte of data is written (=1) or not written (=0).
14
Preliminary Data Sheet E0260E40 (Ver. 4.0)
ELPIDA [ ELPIDA MEMORY ]
