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usb to rs485 full duplex communication
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temtronic



Joined: 01 Jul 2010
Posts: 9081
Location: Greensville,Ontario

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PostPosted: Fri Mar 20, 2020 2:34 pm     Reply with quote

More puzzle... in the post with 4 'onedrive pictures' there are 2 with a USB adapter. It has USB connector, a 28pin IC, an 8 pin (on bottom) and a 4 pin vertical header.
The top of the PCB, near the connector says USB......85. I think it might be a USB to RS485 adapter. Another picture shows it connected to an LCD display and laptop.
If it really is a USB<> RS485 adapter, then there is no easy way to adapt/convert it into a USB<> RS488 adapter.
The 4th picture is on a 40pin PIC and MAX488 and that can't be the schematic for the adapter......
So I'm wondering if the problem is in needing to connect the USB 'module' to the 40pin PIC/max488 ?

It'd probably be easy IF we were sitting at his bench.......

Jay
ertansuluagac



Joined: 13 Jul 2017
Posts: 135
Location: IZMIR

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PostPosted: Mon Mar 23, 2020 5:06 am     Reply with quote

USB-TTL converter, I connected max488 to the card. It worked very smoothly. I also can't see an error on my card. But I couldn't run it.
https://www.robitshop.com/urun/usb-ttl-seri-donusturucu-kart-pl2303?gclid=EAIaIQobChMI5ruJi7qw6AIVzRsYCh2i9QMAEAQYAiABEgKQ1fD_BwE
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temtronic



Joined: 01 Jul 2010
Posts: 9081
Location: Greensville,Ontario

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PostPosted: Mon Mar 23, 2020 5:31 am     Reply with quote

Please perform these simple 'loopback' test.

Test #1. Connect a jumper from USBTTL - TX pin to USBTTL - RX pin. Run your PC terminal program, every key pressed on the PC KBD should go to the USB module, out the TX pin, back into the RX pin, through the USB port and onto the PC screen. This will CONFIRM the USB module is working.

Test #2. Remove jumper from #1 test, connect your MAX488 chip. ADD two jumpers, A to X, B to Y. Now, any key pressed should go all the way to the 488 pins, 'loopback' and be displayed on the PC screen. This will CONFIRM the MAX488 is working properly.

Test #3. Connect to your other 'device'. Be sure to setup the PC terminal program for the correct baudrate, bits, etc. to match the other 'device'. You may need to add/delete any bias or termination resistors.

Please post information as to what the 'device' is you're connecting to. A 'link' to the datasheet would really help. It could be something simple. The 'device' might default to 9600 baud but your terminal defaults to 57600. That doesn't work, it might show 'garbage' characters. Changing the 57600 to 9600 should fix it.
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