CY28400 Cypress Semiconductor, CY28400 Datasheet - Page 8

• Manufacturer Part Number: CY28400
• Description: 100-MHz Differential Buffer for PCI Express and SATA
• Manufacturer: Cypress Semiconductor

Document #: 38-07591 Rev. **
Output Enable Clarification
The outputs may be disabled in two ways, via writing a ‘0’ to
SMBus register bit corresponding to output of interest or by
asserting an OE input pin low. In both methods, if SMBus
registered bit has been written low or the OE pin is low or both,
the output of interest will be three-stated. The assertion and
deassertion of this signal is asynchronous.
Table 6. OE Functionality
OE Assertion
All differential outputs that were three-stated will resume
normal operation in a glitch-free manner. The maximum
latency from the assertion to active outputs is between 2–6 DIF
clock periods. In addition, DIFT clocks will be driven high within
10 ns of OE assertion to a voltage greater than 200 mV.
OE Deassertion
The impact of de- asserting OE is each corresponding output
will transition from normal operation to three-state in a
glitch-free
deassertion to three-stated outputs is between 2–6 DIF clock
periods.
OE (Pin)
DIFC(Free Running
DIFT(Free Running
DIFC(Free Running
manner.
DIFT(Free Running
DIFC (Stoppable)
DIFT (Stoppable)
DIFC (Stoppable)
DIFT (Stoppable)
SRC_STOP#
SRC_STOP#
1
1
0
0
PWRDWN#
PWRDWN#
(Transition from ‘0’ to ‘1’)
(Transition from ‘1’ to ‘0’)
The
maximum
Figure 7. SRC_STOP# = Three-state, PWRDWN# = Three-state
Figure 6. SRC_STOP# = Three-state, PWRDWN# = Driven
OE (SMBus Bit)
latency
1
0
1
0
from
the
SRC_DIV2# Clarification
The SRC_DIV2# feature is used to configure the DIF output
mode to be equal to the SRCT_IN input frequency or half the
input frequency in a glitch-free manner. The SRC_DIV2#
function may be implemented by writing a ‘0’ to SMBus register
bit.
SRC_DIV2# Assertion
The impact of writing a ‘0’ to the SRC_DIV/2 register bit is all
DIF outputs will transition cleanly in a glitch-free manner from
normal operation (output frequency equal to input) to half the
input frequency within 2–6 DIF clock periods.
Three-state
Three-state
Three-state
Normal
DIFT
1mS
Three-state
Three-state
Three-state
1mS
Normal
DIFC
CY28400
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