Datasheet

RXD
CANH
CANL
V /2
CC
Recessive
Logic H
Dominant
Logic L
Recessive
Logic H
Time, t
Typical Bus Voltage (V)
Normal & Silent Mode
CANL
CANH
V
diff(D)
V
diff(R)
4
3
2
1
SN65HVD255
SN65HVD256, SN65HVD257
www.ti.com SLLSEA2C –DECEMBER 2011–REVISED SEPTEMBER 2013
FUNCTIONAL DESCRIPTION
OPERATING MODES
The device has two main operating modes: normal mode and silent mode. Operating mode selection is made via
the S input pin.
Table 1. Operating Modes
S Pin MODE DRIVER RECEIVER RXD Pin
LOW Normal Mode Enabled (ON) Enabled (ON) Mirrors Bus State
(1)
HIGH Silent Mode Disabled (OFF) Enabled (ON) Mirrors Bus State
(1) Mirrors bus state: low if CAN bus is dominant, high if CAN bus is recessive.
CAN BUS STATES
The CAN bus has two states during powered operation of the device; dominant and recessive. A dominant bus
state is when the bus is driven differentially, corresponding to a logic low on the TXD and RXD pin. A recessive
bus state is when the bus is biased to V
CC
/ 2 via the high-resistance internal input resistors R
IN
of the receiver,
corresponding to a logic high on the TXD and RXD pins. See Figure 3 and Figure 4.
Figure 3. Bus States (Physical Bit Representation)
Figure 4. Simplified Recessive Common Mode Bias and Receiver
NORMAL MODE
Select the normal mode of device operation by setting S low. The CAN driver and receiver are fully operational
and CAN communication is bi-directional. The driver is translating a digital input on TXD to a differential output
on CANH and CANL. The receiver is translating the differential signal from CANH and CANL to a digital output
on RXD.
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