XR88C681CP Datasheet, PDF (10/99 Pages) Exar Corporation – CMOS DUAL CHANNEL UART (DUART)

XR88C681
AC ELECTRICAL CHARACTERISTICS ^{1, 2, 3} (CONT’D)
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Parameter
Min. Typ. Max. Unit Conditions
Clock Timing (Figure 56) (Cont’d.)

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Transmitter Timing (Figure 57)
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Notes
1._{Parameters are valid over the specified temperature and operating supply ranges. Typical values are 25
C, VCC = 5V and typical}
processing parameters.
2._{All voltages are referenced to ground (GND). For testing, input signal levels are 0.4V and 2.4V with a transition time of 20ns}
maximum. All time measurements are referenced at input voltages of 0.8V and 2.0V as appropriate. See Figure 50.
3._{AC test conditions for outputs: CL = 50pF, RL = 2.7k• to VCC.}
4._{If CS is used as the strobing input, this parameter defines the minimum high time between CSs.}
5._{Consecutive write operations to the same register require at least three edges of the X1 clock between writes.}
6._{This specification imposes a 6 MHz maximum 68000 clock frequency if a read or write cycle follows immediately after the previous}
read or write cycle. A higher 68000 clock can be used if this is not the case.
7._{This specification imposes a lower bound on CS and IACK low, guaranteeing that they will be low for at least one CLK period.}
8._{The minimum high time must be at least 1.5 times the X1/CLK period and the minimum low time must be at least equal to the X1/CLK}
period if either channel’s Receiver is operating in external 1X clock mode.
Specifications are subject to change without notice
ABSOLUTE MAXIMUM RATINGS¹

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1._{Stresses above those listed under the Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rat-}
ing only, and functional operation of the device at these or any other conditions above those indicated in the “Electrical Characteris-
tics” section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.