THVD1500: 20 unit load

This looks as if the circuit pulls DE low when DI is high. Can you show a waveform with DE included?

Hi Ivy,

Can you show a scope shot of DE during this test? As Clemens mentioned it looks as if it could be a mode switch that may be causing that. 

Also are all the nodes on the lines set up like the above schematic - if not can you share how the other nodes are connected? 

Please let me know as the schematic itself doesn't look like there are issues.

Best,

Parker Dodson

Hi Parker,

1. Below are the waveforms of DE and DI.

2.  Yes. All the nodes on the lines set up like the schematic.

3. The customer feedbacks that when the "1" signal is sent, DI is at a low level, THVD1500 is in a receiving state, and the A/B pin of the chip is in an open-drain state. At this time, the "1" signal is maintained by the pull-up and pull-down  resistors.

Due to the limited driving  ability of the pull-up and pull-down resistors, the "1" signal fails to be sent and the communication is abnormal.

The MCU is running the Android system, and it is difficult to control the sending and receiving status of the 485 chip with GPIO.

Could you please help give some suggestions?

Thank you!

Regards,

Ivy

Hi Ivy,

To clarify the issue being seen is that when DI is driven high DE goes low ?

What pull-up resistors are there are DI or DE? I don't see any in the schematic - so I am unsure where the drive strength is coming from?

Also why is there in an issue with controlling the enable pin in the application - this is just a high impedance logic gate? If this is too hard to control in the application switching to a device with auto polarity detection is probably the best move as this will simplify the control of the device and eliminate the need for a reliable voltage source to switch this device in and out if the DE pin cannot be driven properly.

Please let me know!

Best,

Parker Dodson

This is completely schematic .

Hope you early reply

Thanks

HI Clemens，

I have a question about THVD1406.

When the "1" signal is sent and we set it to automatic direction control,the A/B pin of the chip is in an open-drain state?

This is described in the first line of the table. The A/B pins are high/low for a certain time, then are disabled.

Hi Clemens，

What is t(device-auto-dir)? I can't find it discreption in THVD1406 datasheet.How long time is it?

This is specified in section 6.8.

Thank you 

Hi Zheng,

If you have any other questions on any other parts please start a new thread.

Thank you.

-Parker