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DQLMX3

DQLMY0

DQLMY3

DQLMY2

DB3

DQLMX2

DB2

DQ[23:31]/DM3/DQS3

DQ[16:23]/DM2/DQS2

DQLMX1

DB1

DB0

DQLMX0

DQ[8:15]/DM1/DQS1

DQ[0:7]/DM0/DQS0

DQLMY1

DB0 - DB3 represent data bytes 0 - 3.

AM3894

AM3892

www.ti.com

SPRS681A – OCTOBER 2010 – REVISED MARCH 2011

Table 8-24. CK and ADDR_CTRL Routing Specification (continued)

NO.

PARAMETER

MIN

TYP

MAX

UNIT

Center-to-center CK to other DDR3 trace spacing(9)

Center-to-center ADDR_CTRL to other DDR3 trace spacing(9)(10)

Center-to-center ADDR_CTRL to other ADDR_CTRL trace spacing(9)

CK center-to-center spacing(11)

CK spacing to other net(9)

Rcp(12)

Zo-1

Zo+

Rtt(12)(13)

Zo-5

Zo+5

(9)

Center-to-center spacing is allowed to fall to minimum (w) for up to 1250 mils of routed length.

(10) The ADDR_CTRL net class of the other DDR EMIF is considered other DDR3 trace spacing.

(11) CK spacing set to ensure proper differential impedance.

(12) Source termination (series resistor at driver) is specifically not allowed.

(13) Termination values should be uniform across the net class.

8.3.2.16.2 DQS and DQ Routing Specification

Skew within the DQS and DQ/DM net classes directly reduces setup and hold margin and thus this skew

must be controlled. The only way to practically match lengths on a PCB is to lengthen the shorter traces

up to the length of the longest net in the net class and its associated clock. As with CK and ADDR_CTRL,

a reasonable trace route length is to within a percentage of its Manhattan distance. DQLMn is defined as

DQ Longest Manhattan distance n, where n is the byte number. For a 32-bit interface, there are four

DQLMs, DQLM0-DQLM3. Likewise, for a 16-bit interface, there are two DQLMs, DQLM0-DQLM1.

NOTE

It is not required, nor is it recommended, to match the lengths across all bytes. Length

matching is only required within each byte.

Given the DQS and DQ/DM pin locations on the MPU and the DDR3 memories, the maximum possible

Manhattan distance can be determined given the placement. Figure 8-39 shows this distance for four

loads. It is from this distance that the specifications on the lengths of the transmission lines for the data

bus are determined. For DQS and DQ/DM routing, these specifications are contained in Table 8-25.

There are four DQLMs, one for each byte (32-bit interface). Each DQLM is the longest Manhattan distance of the

byte; therefore:

DQLM0 = DQLMX0 + DQLMY0

DQLM1 = DQLMX1 + DQLMY1

DQLM2 = DQLMX2 + DQLMY2

DQLM3 = DQLMX3 + DQLMY3

Figure 8-39. DQLM for Any Number of Allowed DDR3 Devices

Peripheral Information and Timings

181

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