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7–20 Initialization and Configuration
21264/EV68A Hardware Reference Manual
Phase-Lock Loop (PLL) Functional Description
Table 7–12 shows the allowable ClkIn_x frequencies for a given operating frequency
of the 21264/EV68A and the Y
div
divider. For example, to set the 21264/EV68A GCLK
frequency to 500 MHz with a ClkIn_x frequency of 166.7 MHz, the system must select
aY
div
divider of 3 by placing the value 0011
2
on pins IRQ_H[3:0].
Table 7–12 Differential Reference Clock Frequencies in Full-Speed Lock
7.11.2.4 Power-Up/Reset Clocking
During the power-up/reset sequence, when not in PLL bypass mode, there may be a
period of time when ClkIn_x is not yet running, but there is a voltage on PLL_VDD.
The signal DCOK_H is deasserted until power is good throughout the system. The
10% to 90% rise time of DCOK_H should be less than 2 ns. The deasserted state of
DCOK_H and the presence of PLL_VDD causes the PLL to generate a global clock
that is distributed throughout the 21264/EV68A with a frequency range of 1 MHz to
500 MHz. The presence of the global clock during this period avoids permanent dam-
age to the 21264/EV68A.
GCLK Reference Clock Frequency (MHz) for Y
div
Dividers
1
1
Divider 16 is out of range for the 21264/EV68A and reserved for future use. Valid reference clock
(ClkIn_x) frequencies for the 21264/EV68A are specified in the range from 80 to 200. Divider values
that are out of that range are displayed as a dash “—”.
Period
(ns)
Frequency
(MHz)
3
2
2
Dividers of 1 and 2 are to be used only in a PLL test mode.
4567891011121314
15 16
2.5400 133.310080——————
—————
2.4416.7 138.9104.283.3——————
—————
2.3434.8 144.9108.787.0——————
—————
2.2454.5 151.2113.690.9——————
—————
2.1476.2 158.7119.095.2——————
—————
2.0500 166.7125.010083.3—————
—————
1.9526.3 175.4131.6105.387.7—————
—————
1.8555.6 185.2138.9111.192.6—————
—————
1.7588.2 196.1147.1117.698.084.0————
—————
1.6625 —156.3125.0104.289.3————
—————
1.5 666.7 — 166.7 133.3 111.1 95.2 83.3 — — —
—————
1.4 714.3 — 178.6 142.9 119.1 102.0 89.3 — — —
—————
1.3 769.2 — 192.3 153.8 128.2 109.9 96.2 85.5 — —
—————
1.2 833.3 — — 166.7 138.9 119.0 104.2 92.6 83.3 —
—————
1.1 909.1 — — 181.8 151.5 129.9 113.6 101 90.9 —
—————
1.0 1000 — — 200 166.7 142.9 125 111,1 100 90.9 83.3
————
0.91111.1 ———185.2158.7138.9123.5111.1101.0 92.6 85.5
———
0.81250 ————178.6156.3138.9125113.6104.2 96.2 89.3
83.3 —