BOARD LAYOUT

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Release B

This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

6.3.4 Address & Control Signals

This group encompasses the memory address

MA[12:0], bank address BA[0,1], RAS, CAS and

write enable WE signals. The load of the DIMM

module on these signals is the most important

oneand depends upon the type of SDRAM com-

ponents used (x4, x8 or x16) and whether the

DIMM module is single or dual row. The capacitive

loading of the SDRAM inputs alone for an x8 sin-

gle row DIMM will be about 30-40pF. An equiva-

lent circuit for the timing simulation is shown in

Figure 6-14 Most of the delays are due to the PCB

traces and loading rather than the pad itself.

6.3.5 Chip Select Signals (CS#[3:0])

There are 4 chip select pins per DIMM. Chip se-

lects 0 and 2 are always used to select the first

row of SDRAMs and chip selects 1 and 3 select

the second row on dual bank SDRAMs. The chip

select outputs only have to drive one DIMM each

6.3.6 Data Write (MD[63:0])

The load on the data signals is much lower than

the address/control signals for an unbuffered

DIMM. For a registered DIMM the data signals are

the only memory pins of the DIMM which are not

registered. For the design to get maximum benefit

from using registered DIMMs the timings should

be compared to the timings for registered DIMMs

for the other pins..

Figure 6-14. Address/control equivalent circuit

Rterm

100mm

(0.7ns)

10mm

Figure 6-15. CS# equivalent circuit

130mm

(0.9ns)

CS[0]

CS[2]

Figure 6-16. Data write equivalent circuit

125mm

(0.9ns)

10mm