DS89C386 Datasheet, PDF (5/10 Pages) National Semiconductor (TI) – Twelve Channel CMOS Differential Line Receiver

Parameter Measurement Information (Continued)
DS012085-5
C_L Includes load and test jig capacitance.
S1 = V_CC for t_PZL, and t_PLZ measurements.
S1 = GND for t_PZH, and t_PHZ measurements.
S1 = Open for t_PLH, t_PHL, and t_SK.
FIGURE 2. Test Circuit for Switching Characteristics
FIGURE 3. TRI-STATE Output Enable and Disable Waveforms
Application Information
DS012085-6
* R_T is optional although highly recommended to reduce reflections.
FIGURE 4. Two-Wire Balanced System, RS-422
DS012085-7
SKEW
Skew may be thought of in a lot of different ways, the next
few paragraphs should clarify what is represented by t_SK in
this datasheet and how it is determined. Skew, as used in
this databook, is the absolute value of a mathematical differ-
ence between two propagation delays. This is commonly ac-
cepted throughout the semiconductor industry. However,
there is no standardized method of measuring propagation
delay, from which skew is calculated, of differential line re-
ceivers. Elucidating, the voltage level, at which propagation
delays are measured, on both input and output waveforms
are not always consistant. Therefore, skew calculated in this
datasheet, may not be calculated the same as skew defined
in another. This is important to remember whenever making
a skew comparison.
Skew may be calculated for the DS89C386, from many dif-
ferent propagation delay measurements. They may be clas-
sified into two categories, single-ended and differential.
Single-ended skew is calculated from t_PHL and t_PLH propaga-
tion delay measurements (see Figures 5, 6). Differential
skew is calculated from t_PHLD and t_PLHD differential propaga-
tion delay measurements (see Figures 7, 8).
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