signal of the driver. This is important information because the

receiver will interpret the differential output signal. If the dif-

ferential transitions do not continuously ascend or decend

through the receivers threshold region, errors may occur. Er-

rors may also occur if the transitions are too slow.

In addition, complementary skew provides information about

the common mode modulation of the driver. The common

tion may be used as a means for determining EMI affects.

Only “Skew” is specified in this datasheet for the DS89C387.

It refers to the complementary skew of the driver. Comple-

mentary skew is measured at both V3 and V4 (see

Figure 11).

More information can be calculated from the propagation de-

lays. The channel to channel and device to device skew may

be calculated in addition to the types of skew mentioned pre-

viously. These parameters provide timing performance infor-

mation beneficial when designing. The channel to channel

skew is calculated from the variation in propagation delay

from receiver to receiver within one package. The device to

device skew is calculated from the variation in propagation

delay from one DS89C387 to another DS89C387.

For the DS89C387, the maximum channel to channel skew

is9ns(t

low propagation delay. The minimum channel to channel

skew is 0 ns since it is possible for all 12 drivers to have

identical propagation delays. Note, this is best and worst

case calculations used whenever Skew (channel) is not in-

dependently characterized and specified in the datasheet.

The device to device skew may be calculated in the same

way and the results are the same. Therefore, the device to

device skew is 9 ns and 0 ns maximum and minimum re-

spectively.

TABLE 1. DS89C387 Skew Table

Parameter

Min

Typ

Max

Units

Skew (comp.)

0

0.5

3

ns

Skew (channel)

0

9

ns

Skew (device)

0

9

ns

Note Skew (comp.) in

Table 1 is the same as “Skew” in the

datasheet. Also Skew (channel) and Skew (device) are cal-

culations, but are guaranteed by the propagation delay tests.

Both Skew (channel) and Skew (device) would normally be

tighter whenever specified from characterization data.

The information in this section of the datasheet is to help

clarity how skew is defined in this datasheet. This should

help when designing the DS89C387 into most applications.

DS89C387 Equivalent Input/Output Circuits

DS012086-17

FIGURE 12. Driver Output Equivalent Circuit

DS012086-18

FIGURE 13. Driver Input or

Driver Enable Equivalent Circuit

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