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usb to rs485 full duplex communication
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ertansuluagac



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PostPosted: Fri Mar 20, 2020 3:06 am     Reply with quote

understood. But I pressed it as a printed circuit. I have to solve this problem. Let's see if I handle it, I will write the problem_: S
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Ttelmah



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PostPosted: Fri Mar 20, 2020 3:16 am     Reply with quote

That's just the USB connector.

Are you using your units both ends between two PC's?.
You talk about a PC 4-terminal block. It is details of how this is
physically generated that I want.

The circuit you originally posted was for a PIC and full duplex
RS485 connection to this. This needs something else at the other
end. You talk about 'PIC side' and 'PC side. No such thing. To work
and be seen to talk, you either need two PC's with two of these units, or
one of these with a PC and another unit with RS485, and perhaps an LCD.
At times you talk as if you have a PC RS485 connection. If so, what
is generating this?.
So describe what you are actually doing.
ertansuluagac



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PostPosted: Fri Mar 20, 2020 3:35 am     Reply with quote

https://1drv.ms/u/s%21AskLNX_iFag3gfRmuqqSe1dENeQKnw

https://1drv.ms/u/s%21AskLNX_iFag3gfRlYWHvNOB3wbyMsQ

https://1drv.ms/u/s%21AskLNX_iFag3gfRj-H3-Cq1CgfIpcQ

https://1drv.ms/u/s%21AskLNX_iFag3gfRiJefbTnujO1hgxA
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emaxxenon



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PostPosted: Fri Mar 20, 2020 4:05 am     Reply with quote



I saw such a scheme.

A --> 1K --> +
B --> 1K --> GND
ertansuluagac



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PostPosted: Fri Mar 20, 2020 4:21 am     Reply with quote

I don't think the problem is caused by resistors. The problem is related to max488.
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PCM programmer



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PostPosted: Fri Mar 20, 2020 5:09 am     Reply with quote

ertansuluagac wrote:

https://1drv.ms/u/s%21AskLNX_iFag3gfRlYWHvNOB3wbyMsQ

Your schematic shows 120 ohm terminator resistors on both the transmit
and the receive pins. But the example schematic in the MAX488 datasheet
shows resistors only on the receive side. Why do you have them on the
transmit side ?

See Figure 2 on page 8 of the data sheet:
https://datasheets.maximintegrated.com/en/ds/MAX1487-MAX491.pdf

Look at this Maxim page on cable termination:
https://www.maximintegrated.com/en/design/technical-documents/tutorials/7/763.html
Scroll down to Figure 5. It shows two oscilloscope drawings. The left
side is for 54 ohm termination. The signal is badly distorted. The right side
shows 120 ohms, and it's much better.

With your two 120 resistors (one on the transmit side and the other on the
receive side), you will have an effective termination of 60 ohms. Your
signals will be distorted, according to that Maxim website.

Try removing the resistors on the transmit side (pins Z and Y).
ertansuluagac



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PostPosted: Fri Mar 20, 2020 5:34 am     Reply with quote

okay then I will remove the resistance to which Z and Y are connected on the transmission side. I will remove the resistance to which A and B are connected on the receiving side. Will these solve the problem?
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ertansuluagac



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PostPosted: Fri Mar 20, 2020 5:51 am     Reply with quote

I did what he said. The problem still continues.
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PCM programmer



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PostPosted: Fri Mar 20, 2020 5:56 am     Reply with quote

ertansuluagac wrote:

okay then I will remove the resistance to which Z and Y are connected on
the transmission side. I will remove the resistance to which A and B
are connected on the receiving side
. Will these solve the problem?

I did not say to remove the resistor on the receive side.
Keep it.
Ttelmah



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PostPosted: Fri Mar 20, 2020 8:26 am     Reply with quote

Have you got a part number for the USB to TTL module?.
What is the wire you are using?. The termination required depends on this.
ertansuluagac



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PostPosted: Fri Mar 20, 2020 9:47 am     Reply with quote

I sent you everything as a picture. I do not understand what you mean. I don't use USB-TTL. What I use is in the pictures. There is nothing else. I still do not understand there is untold. The wire I use is 0.25
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temtronic



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PostPosted: Fri Mar 20, 2020 1:04 pm     Reply with quote

well I'm confused since you say 'I don't use USB-TTL' but you post pictures and schematics of them....

please post a schematic of exactly what you're using , I want to help, as do others.

I understand English isn't easy, I'm STILL struggling after 66 years !
Thta's why PICTURES are better !!

Jay
ertansuluagac



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PostPosted: Fri Mar 20, 2020 1:24 pm     Reply with quote

I shared all the pictures. What you call USB-TTL tracks. You'd better give an example. I don't understand what you mean. I sent the circuit diagram and pictures.
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Ttelmah



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PostPosted: Fri Mar 20, 2020 2:12 pm     Reply with quote

Er. I'm having a really strong nasty feeling.

When I queried earlier, he gave a part number for a standard USB
connector. His circuit instead shows a USB-TTL module. I'm having
string feelings he doesn't actually have a USB-TTL module, but is connecting
the USB signals directly into the MAX1488 driver. No wonder it won't work...

You have to understand that the MAX1488 needs to connect to a TTL
level async serial signal. If you want to drive this off a PC, you need
a USB to TTL adapter module to generate this. USB cannot directly
connect to RS485 without such an interface.
ertansuluagac



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PostPosted: Fri Mar 20, 2020 2:19 pm     Reply with quote

is this?[url]
https://www.google.com/search?q=usb+ttl+module&bih=657&biw=1366&rlz=1C1SQJL_trTR823TR823&hl=tr&tbm=isch&source=iu&ictx=1&fir=IVOSvlL8OvPa4M%253A%252CLTGsSMC8Oz17-M%252C_&vet=1&usg=AI4_-kRbtoB3-9eCk7LA_8-J8s-xuMdfYg&sa=X&ved=2ahUKEwjk6fPr76noAhVmCWMBHcvVCgUQ9QEwBHoECAoQJA#imgrc=IVOSvlL8OvPa4M:[/url]
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