synchronous rs232 to rs485 trouble

[mg]

Hi:

We have to connect a prototype board that only has asynchronous 9 pin serial outputs and a USB port with a synchronous 15 pin RS485 device.  The communications protocol between the two is SDLC/HDLC.  Our solution involves using a USB to RS232 synchronous serial device that has a Z85C30 built in and a 25 pin output.  This reduces the problem to connecting a 25 pin RS232 synchronous device with a 15 pin synchronous RS485 device.  One of our engineers built a cable interface using Maxim 485 chips and a 9 volt battery.  I've attached the design.  We are not getting output.

Is he missing something?  Better yet, is there an easier solution (off the shelf) to this problem?  Thanks for any and all help.

Mark

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RS232 pinouts

1- protective ground                14
2- TxD Transmitted Data           15 DB   DCE Element Timing
3- RxD Recieve Data                16
4- RTS Request to Send             17 DD   Received Element Timing
5- CTS Clear to Send                18
6- DSR Data Set Ready             19
7- GND Signal Ground/Common  20 DTR  Data Terminal Ready
8- DCD Carrier Detect               21
9                            22
10                           23
11                           24
12                           25
13                             

RS-485 15 pin D-Sub(2 row) pinouts:

1 Tx Data +    (output)
2 Logic Ground
3 Tx Clock +   (output)
4 Logic Ground
5 Rx Data +    (input)
6 Logic Ground
7 Rx Clock +   (input)
8 Logic Ground
9 Tx Data -    (output)
10 Port 1 Disable (0VDC = disable)
11 Tx Clock -  (output)
12 Earth Ground
13 Rx Data -   (input)
14 Reserved
15 Rx Clock -  (input)

[attachment deleted by admin]

[Jan Axelson]

Is this what you have, in order:

proto board with USB host port?

USB A/B cable?

USB/serial adapter with 25-pin connector and serial port that uses 5V logic and synchronous protocol?

your adapter - converts between RS-485 differential voltages and 5V logic?

device with 15 pin RS485 full-duplex interface using synchronous protocol?

Jan

[mg]

Yes, that sequence is right.  The USB/Serial adaptor contains the Z85C30 chip that takes input data over USB and wraps it in SDLC protocol (start,stop flags, checksum, zero bit insertion).  Then, the data is passed to a converter shown in the jpeg attachment that should produce the +/- data. 

[Jan Axelson]

Where are you losing the output? What are you using to view the output? Can you test both directions? Can you monitor what's happening at each point along the way with a scope?

Jan

[mg]

We're losing the output at the end of the cable (after the converter) that connects the USB/serial adapter to the device with the 15 pin port.  We don't see the transmit clock pulse.  We're using an oscilloscope.  I'm pretty sure we have clocking problems.  Does the converter we built look correct?  The supplier of the USB/Serial adapter told us to connect pin 15 to 24 because their device has a transmit clock along with the RS-485 device it is connecting to (through our cable).

You don't happen to consult, do you?  We've been at this problem for a while and need to solve it.

[Jan Axelson]

You can see valid 5V logic at both DI inputs, but no differential voltage at the Y-Z outputs? If that's the case, disconnect the 15-pin device and see what you get.

RS-485's minimum differential output voltage is just 1.5V, though the RS-485 input needs to see just a 200 mV difference.

I'll be busy finishing up a book project for the next few weeks so no time for new projects.

Jan

[bahnfire]

Any update to this? I am looking at building the same cable solution to monitor the SDLC/485 line on a TS2.