AM4376 datasheet(192/261 Pages) TI

192 / 261 page

AM4376, AM4377, AM4378, AM4379

SPRS851B – JUNE 2014 – REVISED APRIL 2015

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5.12.8.2.1.6 Routing Specification

5.12.8.2.1.6.1 CK and ADDR_CTRL Routing Specification

Skew within the CK and ADDR_CTRL 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. A metric to establish this maximum length

is Manhattan distance. The Manhattan distance between two points on a PCB is the length between the points

when connecting them only with horizontal or vertical segments. A reasonable trace route length is to within a

percentage of its Manhattan distance. CACLM is defined as Clock Address Control Longest Manhattan distance.

Given the clock and address pin locations on the device and the DDR3 memories, the maximum possible

Manhattan distance can be determined given the placement. Figure 5-76 shows this distance for two loads. It is

from this distance that the specifications on the lengths of the transmission lines for the address bus are

determined. CACLM is determined similarly for other address bus configurations; that is, it is based on the

longest net of the CK and ADDR_CTRL net class. For CK and ADDR_CTRL routing, these specifications are

contained in Table 5-59.

192

Specifications

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AM4376 Datasheet(PDF) 192 Page - Texas Instruments