I'm not sure I understand what is happening. Does the ISU 512 show it is dialing some device, or does the CODEC which is connected to the serial interface of the ISU 512 continuously show an "Incoming Call"?
What does the front panel of the ISU 512 show? If it shows BONDING then the call is connected and may not be hanging up when you hang up from the CODEC. If this is the case, then look at the ISU 512 and see what the DTR is set to (under CONFIG and DTE OPTIONS). DTR is what is used by the end equipment to hang up the call, so if DTR is set to IGNORE then you must hang up from the front pannel because the ISU is not looking at the DTR signal in order to hang up the call. You can try setting it to either "Idle when Off" or "Ignore/Idle" to see if that makes a difference.
If DTR is set to "Dial #0 if ON" then it is programmed to dial stored number 0 when DTR is present.
If the ISU 512 is not hanging up the call, this will also cause your local CODEC to show an incoming call (because the previous call never hung up).
If this is not what is happening, then I need a better description of what exactly is happening.
Thank you for responding.
I have a Tandberg 6000MXP conencted to the ISU512, and as soon as the ISU512 comes online, the codec continuously shows "Incoming Call". The front front of the ISU512 doesn't show any status, just the normal screen showing my lines are ready. I tried hanging up through the ISU512, but does nothing. I hang up or decline the call through the CODEC, but immediately after gets the same incoming call. I turn the ISU512 and the calling stops.
I will check the DTR settings next time I'm on site.
Also, is there a replacement product for the ISU512?
I'm afraid there is no replacement product for the ISU 512.
If the Tandberg is showing an "Incoming Call" then it is interpreting a signal from the ISU 512 as an indication of an inbound call. What LEDs are lit on the front of the ISU?
I have seen where some CODECs use Clear To Send (CTS) as an indicator for an inbound call. (CTS is abbreviated to CS on the LED display.) If this is the case with the Tandberg, then you can adjust this on the ISU by going under CONFIG and DTE OPTIONS to the CTS and change it from FOLLOW RTS (or FORCED CTS) to FOLLOW CD. This should drop the CTS signal and hopefully clear the "Incoming call" from the Tandberg.
Since we haven't heard anything back from you, I'm going to mark this question as "assumed answered". If you have additional questions feel free to continue the discussion.