SN65HVD1780: SN65HVD1780 enable

Vidhya Jeyapaul

Part Number: SN65HVD1780
Other Parts Discussed in Thread: THVD1406

Hi Team,

We are using SN65HVD1780 part in our design. Refer to the circuit below.

1. DE and RE are always enabled and are not controlled by MCU. Will there be any issue in transmitting and receiving half duplex communication?

2. If there is any concern, drop in replacement to full duplex parts are available? without design change?

Please revert.

Thanks,

Vidhya

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 321890 points

As long as DE is high, this device will transmit on the bus, and no other node can send anything.

A full-duplex transceiver has separate differential bus signals for sending and receiving; this would require two additional pins (or pins in place of the DE/RE pins). So a P2P change is not possible.

0 Vidhya Jeyapaul over 4 years ago in reply to Clemens Ladisch

Intellectual 780 points

ok. will there be a concern if there is one to one communication(with only one driver and one receiver)?

What if DE is left open? With RE enabled, only receive operation can be performed?

Please revert.

0 Clemens Ladisch over 4 years ago in reply to Vidhya Jeyapaul

Guru 321890 points

As long as DE is high, the only possible communication is from this driver to other receivers.

When DE is open, the driver is always disabled, and only receiving is possible at this node.

0 Eric Schott1 over 4 years ago in reply to Clemens Ladisch

TI__Guru 53535 points

Hi Vidhya,

For a half-duplex implementation, it is common for DE to be controlled by the MCU so that the direction of communication can be changed. This way DE can be driven high when the local node is transmitting, then DE driven low when receiving. The receiver can be left enabled in both cases to always reflect the bus state, or the /RE line can be shared with DE so that it is only active when the node is not actively controlling the bus.

Alternatively, a full-duplex device may be used to allow the driver to remain active persistently. However, like Clemens mentioned, this requires a separate differential pair for the unidirectional signals, and thus a different pinout.

Let us know if you have any more questions.

Regards,
Eric Schott

0 Clemens Ladisch over 4 years ago in reply to Vidhya Jeyapaul

Guru 321890 points

You might be interested in the upcoming THVD1406 device with automatic direction control.

0 Vidhya Jeyapaul over 4 years ago in reply to Eric Schott1

Intellectual 780 points

Thanks Clemens, Eric.

So I can configure as 3rd one with only DE controlled from MCU and RE kept always enabled (active low)?

Kindly confirm.

Thanks and Regards,

Vidhya

0 Vidhya Jeyapaul over 4 years ago in reply to Clemens Ladisch

Intellectual 780 points

Hi Clemens,

with THVD1406 still SHDN pin need to be controlled by MCU right?

How is it automated? Kindly clarify.

Thanks,

Vidhya

0 Eric Hackett over 4 years ago in reply to Vidhya Jeyapaul

TI__Guru 74372 points

Vidhya,

In the THVD1406, if D is left open/high for longer than tdevice-auto-dir, the receiver will automatically be enabled. So, on the THVD1406, you can tie both SHDN and RE high and control the driver and receiver using the D pin connected to the MCU. When being driven by a toggling waveform, the D pin will keep the device in driving mode. If D is left high meaning no messages are coming through, the THVD1406 will automatically switch to receiver mode.

Regards,

Eric Hackett

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SN65HVD1780: SN65HVD1780 enable