Datasheet

SN65HVD05, SN65HVD06
SN75HVD05, SN65HVD07
SN75HVD06, SN75HVD07
www.ti.com SLLS533E –MAY 2002– REVISED AUGUST 2009
FUNCTION TABLES
Table 1. DRIVER
INPUT ENABLE OUTPUTS
D DE A B
H H H L
L H L H
X L Z Z
Open H H L
X Open Z Z
Table 2. RECEIVER
(1)
DIFFERENTIAL INPUTS ENABLE OUTPUT
V
ID
= V
A
– V
B
RE R
V
ID
≤ –0.2 V L L
–0.2 V < V
ID
< –0.01 V L ?
–0.01 V≤ V
ID
L H
X H Z
Open Circuit L H
Short Circuit L H
IDLE Bus L H
X Open Z
(1) H = high level; L = low level; Z = high impedance; X = irrelevant;
? = indeterminate
Receiver Failsafe
The differential receiver is “failsafe” to invalid bus states caused by:
• open bus conditions such as a disconnected connector,
• shorted bus conditions such as cable damage shorting the twisted-pair together, or
• idle bus conditions that occur when no driver on the bus is actively driving
In any of these cases, the differential receiver outputs a failsafe logic High state, so that the output of the
receiver is not indeterminate.
Receiver failsafe is accomplished by offsetting the receiver thresholds so that the “input indeterminate” range
does not include zero volts differential. To comply with the RS-422 and RS-485 standards, the receiver output
must output a High when the differential input V
ID
is more positive than +200 mV, and must output a Low when
the V
ID
is more negative than -200 mV. The receiver parameters which determine the failsafe performance are
V
IT+
and V
IT-
and V
HYS
. As seen in the Receiver Electrical Characteristics table, differential signals more negative
than -200 mV will always cause a Low receiver output. Similarly, differential signals more positive than +200 mV
will always cause a High receiver output.
When the differential input signal is close to zero, it will still be above the V
IT+
threshold, and the receiver output
is High. Only when the differential input is more negative than V
IT-
will the receiver output transition to a Low
state. So, the noise immunity of the receiver inputs during a bus fault condition includes the receiver hysteresis
value V
HYS
(the separation between V
IT+
and V
IT-
) as well as the value of V
IT+
.
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