Rainbow Electronics ATA6631 - Manual (Page 4)

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9165A–AUTO–11/09
ATA6629/ATA6631
3.7 Input/Output (TXD)
In Normal Mode the TXD pin is the microcontroller interface to control the state of the LIN output.
TXD must be pulled to ground in order to drive the LIN bus low. If TXD is high or unconnected
(internal pull-up resistor), the LIN output transistor is turned off and the bus is in the recessive
state. During Fail-safe Mode, this pin is used as output and is signalling the fail-safe source.
3.8 Dominant Time-out Function (TXD)
The TXD input has an internal pull-up resistor. An internal timer prevents the bus line from being
driven permanently in the dominant state. If TXD is forced to low longer than t
DOM
> 27 ms, the
LIN bus driver is switched to the recessive state. Nevertheless, when switching to Sleep Mode,
the actual level at the TXD pin is relevant.
To reactivate the LIN bus driver, switch TXD to high (> 10 µs).
3.9 Output Pin (RXD)
This pin reports the state of the LIN bus to the microcontroller. LIN high (recessive state) is
reported by a high level at RXD; LIN low (dominant state) is reported by a low level at RXD. The
output has an internal pull-up resistor with typically 5 k
Ω
to V
CC
. The AC characteristics are mea-
sured with an external load capacitor of 20 pF.
The output is short-circuit protected. In Unpowered Mode (that is, V
S
= 0V), RXD is switched off.
3.10 Enable Input Pin (EN)
The Enable Input pin controls the operation mode of the device. If EN is high, the circuit is in
Normal Mode, with transmission paths from TXD to LIN and from LIN to RXD both active. The
VCC voltage regulator operates with 3.3V/5V/50 mA output capability.
If EN is switched to low while TXD is still high, the device is forced to Silent Mode. No data trans-
mission is then possible, and the current consumption is reduced to I
VS
typ. 40 µA. The VCC
regulator has its full functionality.
If EN is switched to low while TXD is low, the device is forced to Sleep Mode. No data transmis-
sion is possible, and the voltage regulator is switched off.