W134M_05 Datasheet, PDF (5/12 Pages) Cypress Semiconductor – Direct Rambus™ Clock Generator

W134M/W134S
Table 4. Bypass and Test Mode Selection
Mode
Bypclk
S0 S1 (int.) Clk
ClkB
Normal
0 0 Gnd PAclk PAclkB
Output Test (OE) 0 1
–
Hi-Z Hi-Z
Bypass
1 0 PLLclk PLLclk PLLclkB
Test
1 1 Refclk Refclk RefclkB
Table 5 shows the logic for selecting the Power-down mode,
using the PwrDnB input signal. PwrDnB is active LOW
(enabled when 0). When PwrDnB is disabled, the DRCG is in
its normal mode. When PwrDnB is enabled, the DRCG is put
into a powered-off state, and the Clk and ClkB outputs are
three-stated.
Table 5. Power-down Mode Selection
Mode
Normal
Power-down
PwrDnB
1
0
Clk
PAclk
GND
ClkB
PAclkB
GND
Table of Frequencies and Gear Ratios
Table 6 shows several supported Pclk and Busclk
frequencies, the corresponding A and B dividers required in
the DRCG PLL, and the corresponding M and N dividers in the
gear ratio logic. The column Ratio gives the Gear Ratio as
defined Pclk/Synclk (same as M and N). The column F@PD
gives the divided down frequency (in MHz) at the Phase
Detector, where F@PD = Pclk/M = Synclk/N.
State Transitions
The clock source has three fundamental operating states.
Figure 4 shows the state diagram with each transition labelled
A through H. Note that the clock source output may NOT be
glitch-free during state transitions.
Upon powering up the device, the device can enter any state,
depending on the settings of the control signals, PwrDnB and
StopB.
In Power-down mode, the clock source is powered down with
the control signal, PwrDnB, equal to 0. The control signals S0
and S1 must be stable before power is applied to the device,
and can only be changed in Power-down mode (PwrDnB = 0).
The reference inputs, V_DDR and V_DDPD, may remain on or may
be grounded during the Power-down mode.
Table 6. Examples of Frequencies, Dividers, and Gear Ratios
Pclk Refclk Busclk Synclk A B M N Ratio F@PD
67 33
267
67 8 1 2 2 1.0
33
100 50
300
75 6 1 8 6 1.33 12.5
100 50 400 100 8 1 4 4 1.0 25
133 67
267
67 4 1 4 2 2.0
33
133 67 400 100 6 1 8 6 1.33 16.7
The control signals Mult0 and Mult1 can be used in two ways.
If they are changed during Power-down mode, then the
Power-down transition timings determine the settling time of
the DRCG. However, the Mult0 and Mult1 control signals can
also be changed during Normal mode. When the Mult control
signals are “hot-swapped” in this manner, the Mult transition
timings determine the settling time of the DRCG.
In Normal mode, the clock source is on, and the output is
enabled.
Table 7 lists the control signals for each state.
Table 7. Control Signals for Clock Source States
State
Power-down
Clock Stop
Normal
PwrDnB
0
1
1
StopB
X
0
1
Clock
Source
OFF
ON
ON
Output
Buffer
Ground
Disabled
Enabled
Figure 5 shows the timing diagrams for the various transitions
between states, and Table 8 specifies the latencies of each
state transition. Note that these transition latencies assume
the following.
Refclk input has settled and meets specification shown in the
Operating Conditions table.
The Mult0, Mult1, S0 and S1 control signals are stable.
VDD Turn-On
M
VDD Turn-On
G
J
L
Test
N
B
K
A
VDD Turn-On
Power-Down
Normal
E
D
C
F
Clk Stop
Figure 4. Clock Source State Diagram
Document #: 38-07426 Rev. *C
VDD Turn-On
H
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