Intel
®
81341 and 81342—DDR SDRAM Memory Controller
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
652
Order Number: 315037-002US
7.8.24
DDR RCOMP Control Register — DRCR
This register provides controls for the DDR RCOMP state machine. The RCOMP state
machine is used to dynamically adjust the drive strength and the slew rate in order to
compensate for temperature and voltage variations. The RCOMP state machine
operates using the values provided in the
“DDR RCOMP Control Register — DRCR” on
and
“RCOMP Pad Drive Strength Select — RPDSR” on page 654
Table 397. DDR RCOMP Control Register — DRCR (Sheet 1 of 2)
Bit
Default
Description
31:14
00000H
Reserved
13
0
2
When this bit is set, the slew rate manual override values are used. When this bit is cleared, the slew
rate is derived from the drive strength (normal operation).
12:11
11
2
ODT Enable: Enables ODT for the DQ input pads by selecting 75 ohms or 150 ohms ODT drive strength.
The RCOMP state machine uses the selected value to dynamically adjust the drive strength and the slew
rate of the DQ input pads.
00
2
ODT is disabled
10
2
selects 150 ohms ODT drive strength (same as 01
2
)
01
2
selects 150 ohms ODT drive strength (same as 10
2
)
11
2
selects 75 ohms ODT drive strength
10:09
01
2
15 Ohm Adjust Control
: This field provides control to further adjust the value for all the 15 ohm drive
strength selection made using
“RCOMP Pad Drive Strength Select — RPDSR” on page 654
00
2
13.7 ohm
01
2
15 ohm
10
2
16.4 ohm
11
2
Reserved.
08:07
10
2
21 Ohm Adjust Control
: This field provides control to further adjust the value for all the 21 ohm drive
strength selection made using
“RCOMP Pad Drive Strength Select — RPDSR” on page 654
00
2
17.9 ohm (
Recommended value for Unbuffered DIMMs
).
01
2
19.4 ohm
10
2
21 ohm
11
2
Reserved.
06:05
01
2
25 Ohm Adjust Control
: This field provides control to further adjust the value for all the 25 ohm drive
strength selection made using
“RCOMP Pad Drive Strength Select — RPDSR” on page 654
00
2
23 ohm
01
2
25 ohm
10
2
27.2 ohm
11
2
Reserved.
04:03
01
2
35 Ohm Adjust Control
: This field provides control to further adjust the value for all the 35 ohm drive
strength selection made using
“RCOMP Pad Drive Strength Select — RPDSR” on page 654
00
2
32.1 ohm
01
2
35 ohm
10
2
38.2 ohm
11
2
Reserved.
PCI
IOP
Attributes
Attributes
28
24
20
16
12
8
4
0
31
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rv
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
rw
na
Attribute Legend:
RV = Reserved
PR = Preserved
RS = Read/Set
RW = Read/Write
RC = Read Clear
RO = Read Only
NA = Not Accessible
Intel XScale
®
microarchitecture Local
Bus offset
+2000H