AM1808_1112 Datasheet, PDF (119/262 Pages) Texas Instruments – AM1808 ARM Microprocessor

AM1808
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SPRS653C – FEBRUARY 2010 – REVISED DECEMBER 2011
Figure 5-23 shows the routing for the DQGATE net class. Table 5-36 contains the routing specification.
A1
T
F
T
A1
Figure 5-23. DQGATE Routing
Table 5-36. DQGATE Routing Specification
NO. PARAMETER
1 DQGATE Length F
2 Center to center DQGATE to any other trace spacing
MIN
4w ⁽²⁾
TYP
CKB0B ⁽¹⁾
3 DQS/D nominal trace length
4 DQGATE Skew⁽³⁾
DQLM-50
DQLM
(1) CKB0B1 is the sum of the length of the CK net plus the average length of the DQS0 and DQS1 nets.
(2) w = PCB trace width as defined in Table 5-27.
(3) Skew from CKB0B1
MAX
DQLM+50
100
UNIT
Mils
Mils
5.11.3.12 MDDR/DDR2 Boundary Scan Limitations
Due to DDR implementation and timing restrictions, it was not possible to place boundary scan cells
between core logic and the IO like boundary scan cells for other IO. Instead, the boundary scan cells are
tapped-off to the DDR PHY and there is the equivalent of a multiplexer inside the DDR PHY which selects
between functional and boundary scan paths.
The implication for boundary scan is that the DDR pins will not support the SAMPLE function of the output
enable cells on the DDR pins and this is a violation of IEEE 1149.1. Full EXTEST and PRELOAD
capability is still available.
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Peripheral Information and Electrical Specifications 119
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