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CY28442ZXC Datasheet(PDF) 11 Page - SpectraLinear Inc |
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CY28442ZXC Datasheet(HTML) 11 Page - SpectraLinear Inc |
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11 / 21 page  CY28442 Rev 1.0, November 21, 2006 Page 11 of 21 CLK_REQ[0:1]# Description The CLKREQ#[A:B] signals are active low input used for clean enabling and disabling selected SRC outputs. The outputs controlled by CLKREQ#[A:B] are determined by the settings in register byte 8. The CLKREQ# signal is a de-bounced signal in that it’s state must remain unchanged during two consec- utive rising edges of SRCC to be recognized as a valid assertion or de-assertion. (The assertion and de-assertion of this signal is absolutely asynchronous). CLK_REQ[A:B]# Assertion (CLKREQ# -> LOW) All differential outputs that were stopped are to resume normal operation in a glitch free manner. The maximum latency from the assertion to active outputs is between 2-6 SRC clock periods (2 clocks are shown) with all SRC outputs resuming simultaneously. All stopped SRC outputs must be driven high within 10 ns of CLKREQ#[1:0] de-assertion to a voltage greater than 200mV. CLK_REQ[A:B]# Deassertion (CLKREQ# -> HIGH) The impact of deasserting the CLKREQ#[A:B] pins is all SRC outputs that are set in the control registers to stoppable via deassertion of CLKREQ#[A:B] are to be stopped after their next transition. The final state of all stopped DIF signals is low, both SRCT clock and SRCC clock outputs will not be driven. PD (Power-down) Clarification The VTT_PWRGD# /PD pin is a dual function pin. During initial power up, the pin functions as VTT_PWRGD#. Once VTT_PWRGD# has been sampled low by the clock chip, the pin assumes PD functionality. The PD pin is an asynchronous active high input used to shut off all clocks cleanly prior to shutting off power to the device. This signal is synchronized internal to the device prior to powering down the clock synthe- sizer. PD is also an asynchronous input for powering up the system. When PD is asserted high, all clocks need to be driven to a low value and held prior to turning off the VCOs and the crystal oscillator. PD (Power-down) – Assertion When PD is sampled high by two consecutive rising edges of CPUC, all single-ended outputs will be held low on their next high to low transition and differential clocks must held high or Tri-stated (depending on the state of the control register drive mode bit) on the next diff clock# high to low transition within 4 clock periods. When the SMBus PD drive mode bit corre- sponding to the differential (CPU, SRC, and DOT) clock output of interest is programmed to ‘0’, the clock output are held with “Diff clock” pin driven high at 2 x Iref, and “Diff clock#” tristate. If the control register PD drive mode bit corresponding to the output of interest is programmed to “1”, then both the “Diff clock” and the “Diff clock#” are tristate. Note the example below shows CPUT = 133 MHz and PD drive mode = ‘1’ for all differential outputs. This diagram and description is applicable to valid CPU frequencies 100,133,166,200,266,333 and 400MHz. In the event that PD mode is desired as the initial power-on state, PD must be asserted high in less than 10 uS after asserting Vtt_PwrGd#. Figure 3. CLK_REQ#[A:B] Deassertion/Assertion Waveform SRCT(stoppable) SRCT(stoppable) SRCC(free running) SRCT(free running) CLKREQ#X |
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