KM416RD8AS-RBM80 datasheet(56/64 Pages) SAMSUNG

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Page 53

KM416RD8AS

Direct RDRAM™

Rev. 0.9 July 1999

Target

Figure 58 also shows the combinational path connecting

SIO0 to SIO1 and the path connecting SIO1 to SIO0 (read

data only). The tPROP1 parameter specified this propagation

delay. The rise and fall times of SIO0 and SIO1 inputs must

be tDR1 and tDF1, measured at the 20% and 80% levels. The

rise and fall times of SIO0 and SIO1 outputs are tQR1 and

tQF1, measured at the 20% and 80% levels.

RSL - Domain Crossing Window

When read data is returned by the RDRAM, imformation

must cross from the receive clock domain (CFM) to the

transmit clock domain (CTM). The tTR parameter permits

the CFM to CTM phase to vary through an entire cycle; i.e.

there is no restriction on the alignment of these two clocks.

A second parameter tDCW is needed in order to describe how

the delay between a RD command packet and read data

packet varies as a function of the tTR value.

Figure 59 shows this timing for five distinct values of tTR.

Case A (tTR=0) is what has been used throughout this docu-

ment. The delay between the RD command and read data is

tCAC. As tTR varies from zero to tCYCLE (cases A through

E), the command to data delay is (tCAC-tTR). When the tTR

value is in the range 0 to tDCW,MAX, the command to data

delay can also be (tCAC-tTR-tCYCLE). This is shown as cases

A’ and B’ (the gray packets). Similarly, when the t TR value

is in the range (tCYCLE+tDCW,MIN) to tCYCLE, the command

to data delay can also be (tCAC-tTR+tCYCLE). This is shown

as cases D’ and E’ (the gray packets). The RDRAM will

work reliably with either the white or gray packet timing.

The delay value is selected at initialization, and remains

fixed thereafter.

Figure 59: RSL Transmit - Crossing Read Domains

CFM

COL

tTR

CTM

DQA/B

tTR=0

tCYCLE

Case A

tTR=0

Case A’

tTR

CTM

DQA/B

tTR=tDCW,MAX

Case B

tTR=tDCW,MAX

Case B’

tTR

CTM

DQA/B

tTR=0.5•t CYCLE

Case C

CTM

DQA/B

tTR=tCYCLE+tDCW,MIN

Case D

tTR=tCYCLE+tDCW,MIN

Case D’

CTM

DQA/B

tTR=tCYCLE

Case E

tTR=tCYCLE

Case E’

tTR

RD a1

Q(a1)

tCAC-tTR

tCAC-tTR-tCYCLE

Q(a1)

tCAC-tTR

tCAC-tTR+tCYCLE

tCAC-tTR

tCAC-tTR+tCYCLE

tCAC-tTR

tCAC -tTR-tCYCLE

tCAC-tTR

•••

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