RS232 serial cable connected to an AMX or a Crestron

I think this report has connection with “RS232 serial cable connected to a PC” on the Knowledge Base.

Some dealers reported that the Status LED of ESP is not turned on and the sound doesn’t come when the RS232 of ESP is connected to an AMX or a Crestron. According to the dealers the AMX or the Crestron of the system which this issue occurred may send some commands to the ESP before the Status LED lit. We informed them the ESP should not be sent some commands before the Status lit.

Then, (I think this has relations with above issue,) I have a few experiences that the Designer PC was not be able to go-online to the ESP which had RS232 connection with an AMX or a Crestron. Once the ESP becomes so, the Designer can’t go-online even if the ESP is rebooted. The remedy of this situation is follows.
1. update the firmware of the ESP to v1.1
2. go-online by the Designer 1.1 with a blank signal flow
3. update the firmware to original version(v2.050)
(It was not resolved only by firmware update with original version.)

Please let me know if someone has any information about it.


You should check to see if there is DC voltage on the AMX/Crestron/PC serial port when in the static or inactive state. (I’m not sure how you officially say this in computer language)

For Example:

The serial port on my IBM/Lenovo docking station has no voltage on the serial output port in the incative state. This works as expected. When this is connected to the ESP serial port, I can turn the ESP on without errors.

On my new Dell docking station, however, I can measure /- 5-7VDC between pins 2&5 and pins 3&5. The ESP ‘hangs’ at start-up. I have no status light and cannot connect with the PC, etc.

My first work-around is to power up the PC then physically connect to the serial port.

The other work-around for the Dell is to have terminal software open and connected (hyper-terminal, Extron Dataviewer, etc) When this software is open and active(connected) I cant the power-up the ESP while physically connected to the port on my Dell. I get the green status light and can connect with the PC. I also get the ‘READY’ string from the ESP telling me it’s up and running properly.

I’m not sure how this will relate to the AMX/Crestron hardware. You may want to have the control program wait to receive the ‘ready’ string from the ESP at start-up to intiate any other command sequences from the control system.

Am I on the right track with the problem?


Hi Kakudo

The cause of the issue described in the Knowledge Base Article is the Rx pin being pulled to ve voltage when the port is idle. This will only cause an issue during the inital boot stage, once booted it is OK. I have specifically tested the ESP connected to both AV2 and CP2 Crestron processors and neither have prevented the ESP from booting normally. I have no experience with AMX with regard to this issue, perhaps someone else is able to confirm if they have come across similar with AMX systems.

As John says Crestron/AMX programmers would typically wait to receive the ‘Ready’ string (or any other response) before issuing commands to the ESP if this is possible.

On the occasions that you were unable to connect with ControlSpace Designer whilst the ESP was connected to an AMX/Crestron system had you disconnected the serial cable while you rebooted the ESP and were still unable to connect? Also what color was the ‘Status’ LED whilst you were unable to connect?

Best regards