ACKSYS DTUS0434 Servercom Firmware For Ethernet and Wi-Fi Port Servers User Guide

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I. INTRODUCTION

The SERVERCOM software allows any port server made by ACKSYS to be used as a distant serial communication port for a TCP/IP compliant computer. SERVERCOM may operate in three distinct modes, depending on needs of the remote application software :

In RFC2217-compliant mode, SERVERCOM allows the remote application software to receive and send data, monitor input control signals, set output control signals, change the data format and baud rate, through the remote computer native serial port interface.This mode is relevant when the remote computer has a RFC2217- compliant client driver which emulates a serial port for the application software. It is especially useful when the application software must be made to use a remote port, but it cannot be changed to support TCP/IP communication (i.e. when the application source code is not available).
For more information about RFC2217, see : http://www.ietf.org/rfc/rfc2217.txt
In RAW mode, SERVERCOM has a much simpler TCP/IP interface which only allows to receive and send data. All the serial communication parameters can be set up locally in the port server through the administration interface.This mode is relevant in all the other cases:
- when the remote computer is another port server in TCP-CLIENT mode;
- when the remote computer has no RFC2217-compliant client driver;
- when the remote application software can be written from scratch to use the TCP/IP SOCKET interface;
In TELNET mode, SERVERCOM allows a standard TELNET client to to receive and send data. This mode is similar to RFC2217, but it does not handle any COM-related operation, only data exchange.

This mode is relevant for testing purposes, and when the device connected to the port server needs only a serial console interface with the user.

In all modes you can use the port server administration interface to set the serial control signals to behave locally; this allows to have a much faster response time for flow control between the port server and the serial device.

The SERVERCOM firmware functions as a network server. This means that it provides serial port service to the network: when the SERVERCOM firmware is in use, the port server just sits there waiting for some remote network device (usually a computer or another port server in network client mode) to call in and use its serial port. In this mode the port server will never attempt on its own to connect to a remote network device.

II. WHEN TO USE THE SERVERCOM FIRMWARE ?

In order to identify the cases where SERVERCOM can be used, it is important to know that the SERVERCOM firmware has the following properties:
• It uses TCP communications on the network side, forbidding undetected data loss at the expense of slower communications.
• It conveys no protocol information in the data exchanged between the remote application software and the device connected to the port server 1.
• It can handle serial communications up to 230400 bauds.
• It can drive and monitor serial control signals, locally or remotely.

The SERVERCOM firmware can be used to solve the following needs:

• Application software using full remote COM port emulation.
• Application software using partial (data only) remote COM port emulation.
• Application software using a TCP SOCKET to exchange data with a serial comm server.
• Tunelling two-ways data between SERVERCOM and TCP-CLIENT.
• Tunnelling MODBUS frames (or other asynchronous protocols) in pointto- point configurations.
• TELNET client used as a serial console to the device connected to the port server.

III. USING SERVERCOM IN RFC2217 MODE

III.1 Configuration

The network configuration, including IP address, netmask, gateway (router) address, DHCP, and so on, is described in the port server user manual.

The SERVERCOM firmware comes with defaults settings for the RFC2217 mode. These settings can be reinstated with the “set default” command. Important settings are:

set serial mode: by default this is set to “set serial mode rcf2217”
set sendtrigger: by default the SERVERCOM firmware sends incoming serial data onto the network after waiting at most 2 milliseconds. Often you will want to change this. See the detailed documentation of this command.
flow control: by default the SERVERCOM firmware uses no local flow control. Often you will want to change this. See the detailed documentation of the “set serial” commands.
set keepalive…: allows the SERVERCOM firmware to detect when the client crashes and thus allows later reconnection from the same or another client.
set reconnect…: allows the (same) network client to establish a new connection, forcing the SERVERCOM firmware to close the previous one. This allows faster recovery of client failure than keepalives.
- Let say that you connect the port server to a device that sends frames of 3 to 100 chars at 1200 bauds, followed by a silence of at least 3 char times. The default sendtrigger will work, but it is not suited for this kind of data since each received char would be sent on the Ethernet in its own frame, loosing a lot of network bandwidth. A better sendtrigger in this case is:
  set sendtrigger idledelay 3c
  
  Do not forget also in this case:
  
  set serial baudrate 1200
- Let say that you connect the port server to a device honors XON/XOFF protocol. Then you can set it in the port server:
  set serial xonxoff use
- Let say that you connect the port server to a device honors RTS/CTS protocol. Then you can set it in the port server:
  set serial rts flow set serial cts flow
  
  Note that this is not required if the remote (network client) computer has a fully compliant RFC2217 driver, since the remote computer can use the RFC2217 protocol to set the flow control remotely.
- Let say that you access the port server from a remote computer that is on the other side of a firewall. Say that this firewall forbids the use of TCP port 2300 but allows TCP port 4000. Then you can set it in the port server:
set serial port 4000

(this is considered a “serial” parameter since it would be different for each serial port, had the port server had more than one serial port).

III.2 Using VIP

VIP is a RFC2217 compliant COM port emulator that allows Windows applications written to use native PC COM ports, to access the port server serial port transparently.
To use it, or other RFC2217 compliant port redirector, the “mode” parameter of the “set serial mode mode” command must be set to “rfc2217“.
The VIP software, more information, and a link to get the latest version are available on the CD-ROM.

VIP Windows COM port redirector software installation
Before installing the redirector software, read the release notes.
Run the executable file on the provided disk. This installs the VIP software, allowing COM port redirection from MSWindows to the port server.
Run the VIP config program from the desktop icon or the start menu.
If needed, stop the VIP service in the “Setup” tab, then click the “scan for devices” button. Fill in the IP range to scan, click “scan” to find the available ACKSYS port servers. Choose one and click “add”.
Note: if your port server does not appear in the scan list, your network may be improperly set or overloaded. You can still close the scanner, select the “virtual port” tab and use the “New” button to manually add a virtual port.
You may enter a custom description for the chosen port server. Then select a COM port name. Other options should be left in their default state.
When you have set up all the virtual ports you need, restart the service with the “setup” tab.
You are now ready to use the port server through port redirection. Just run your application and specify the COM port name that you selected in the previous step.

If you need to write program from scratch, the usual Win32 COMM API can be used. Please refer to the Win32 documentation (included in your development environment) for more details.

III.3 Using the SOCKET interface
The application software can use the SOCKET interface to communicate with a port server put in RFC2217 mode. This involves the capacity to handle the TELNET protocol (transparency and option negotiation) as well as the RFC2217 specific features. Since this is not an easy task, using the SOCKET interface is not recommended in RFC2217 mode.

III.4 Troubleshooting
Before trying to troubleshoot the SERVERCOM firmware in RFC2217 mode, you should insure that the port server is normally visible on the network. Please first refer to the relevant troubleshooting section in the port server user’s manual. In the following instructions it is assumed that you are able to connect to the administration system from the same computer from which you access the port server..

In the “VIP config” setup tab, you can enable a trace log that will appear in the window below. The trace log can also be saved in a file if you need (the file is located in the VIP programs directory). The trace will stay on through reboots. Be warned, this trace slows down the VIP service.

In the “VIP config” virtual port tab, you should see the COM port name that you assigned in the installation. When the port is in use, warning lights are displayed on the left of the name. You can check this by opening the port with Hyperterminal.

If the warning lights do not show up, the address or port given for the port is bad. Also, there may be a problem with the computer’s network parameters : in this case, you cannot PING the port server either.

Enable the trace log. Each time the virtual port is opened by the application, you should see a bunch of messages beginning with these three: “Connecting to…” then “Connection to … successful” then “Purge buffers”. If only the two first connection messages appear, the port server is in RAW mode. You can change this with the « set serial mode » command in the port server administration system. Check that the protocol is set accordingly in the “VIP config” virtual port parameters.
Enter the port server administration mode, check the IP address and network port with the following commands:
show net ip
show serial port
show serial mode

The mode should be “rfc2217”. The display the VIP virtual port parameters window on the remote computer. Check that the “IP address of server” and “port number” are the same as set in the port server. Check that the “protocol” is set to “Telnet”.

If the mode is “rfc2217”, then DTR and RTS should be set to “driven” or “flow”, incoming signals should be set to “ignore” or “flow”, the sendtrigger parameter must be tailored to your needs (the factory default is a good starting point), other serial parameters are irrelevant since they are reset by VIP.

IV. USING SERVERCOM IN RAW MODE

IV.1 Use cases

The “RAW” mode means that the SERVERCOM firmware makes no interpretation of any kind on the data flow in either direction.

You will use the port server in “RAW” mode when either:

You cannot use a COM port redirector (because none is available on your operating system).
You do not need the COM port redirector facilities because your application does not need information about control signals, data errors and so on.

You do not need the COM port redirector facilities because your application is already written and uses a SOCKET interface.In “RAW” mode, the asynchronous serial port of the port server must be fully set up locally, since the client application has no way to advertise the intended use of the character format, baud rate, control signals, etc. You must set all this through the administration commands.
The baud rates are supported by the port server as follows:
The ‘set serial baudrate’ command has a limit of 429,000 bauds.

Any baud rate between 229 bauds and 429,000 bauds can be approximated with an baud skew less than 2.3%
The formula which gives the relative baud skew given the baud rate wantedbaud is:div = E[C/ wantedbaud + 0.5]
realbaud = C/div

relative baud skew = (wantedbaud – realbaud) / wantedbaud

with

C = 15,000,000 (15 MHz)

E[] = integral part function (round-down function)
The fastest achievable transfer rate without character lost is 429,000 bauds when using character format 8×1 (x = e, o, m, s but not n). This speed cannot be sustained for long periods of time.

IV.2 Configuration

In many respects the configuration in raw mode is similar to the configuration in rfc2217 mode. Please refer to the RFC2217 mode configuration.

Howeve the important setting in RAW mode is:
• set serial mode raw: must be set, since the default mode is rcf2217.

IV.3 Using VIP

In many respects the configuration in raw mode is similar to the configuration in rfc2217 mode. Please refer to the RFC2217 mode configuration.

Howeve the important setting in RAW mode is:

set serial mode raw: must be set, since the default mode is rcf2217.

IV.4 Using a redirector for Linux

Third-party open-source redirector software is available for Linux but is not supported by ACKSYS. Search the web for “sredir” or go to
http://packages.debian.org/unstable/source/sredird.

IV.5 Troubleshooting

Troubleshooting with VIP is explained in the RFC2217 mode section. No particular problem is expected in this mode when programing via the SOCKET interface. Should any communication problem arise, the first step of debugging should be:

Try to do the same thing with a standard TELNET client.

IV.6 SOCKET interface example for Linux

The application software can use the SOCKET interface to communicate with a port server put in RAW mode.

To be written

IV.7 SOCKET interface example for Windows

The application software can use the SOCKET interface to communicate with a port server put in RAW mode.
Following is a Visual C++ sample program that receives and resends data to a port server configured in raw mode

Specifications:

Product Name: SERVERCOM Firmware

Compatible with: Ethernet and Wi-Fi Port Servers
Release Version: A.4, April 22, 2009
Manufacturer: ACKSYS

FAQ

1. What is the purpose of SERVERCOM firmware?

The SERVERCOM firmware allows port servers to function as distant serial communication ports for TCP/IP compliant computers.

2. Can SERVERCOM operate in multiple modes?

Yes, SERVERCOM can operate in RFC2217 mode, Raw mode, and Telnet mode depending on the requirements of the application software.

3. How can I set up serial control signals using the port server administration interface?

You can configure the serial control signals locally through the administration interface to ensure faster response time for flow control between the port server and the serial device.

Documents / Resources

ACKSYS DTUS0434 Servercom Firmware For Ethernet and Wi-Fi Port Servers [pdf] User Guide
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References

User Manual

ACKSYS DTUS0434 Servercom Firmware For Ethernet and Wi-Fi Port Servers

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