Reach-Through Serial Ports (DV-200)

Davicom units allow you to communicate with site ancillary or legacy equipment via the Davicom’s own communication link. All you need is to connect each piece of equipment to one of the serial RS-232 reach-through ports on the back of the Davicom, and configure the serial-port communications between the Davicom and the equipment’s legacy software.

Reach-Through Serial Port Access

Configuring your computer’s COM ports

External equipment legacy software requires two free serial ports (COMx & COMy) in your PC (or two virtual ports) for serial-port communications. See or for virtual port drivers for your PC.

As shown in Figure 40 above, DavLink re-routes legacy software communications through the communication channel it uses to communicate with the Davicom. This channel could be another COM port, a modem or TCP/IP link.

To set up the COMx serial port in your computer, go to the DavLink Setup menu, select Communications and in the Reach-Through Communications section, select the computer COM port that DavLink will use to connect with the external equipment legacy software. In the image below, COMx has been set to COM5 as an example.

Reach-Through Communications setup window (computer’s COMx)

Communication Port and Port Speed: Physical or virtual communication port and speed that DavLink will communicate with the external equipment legacy software.

Application Bypasses DavLink: Check this box if you don’t have an extra physical or virtual port. When this box is checked, DavLink will release its communication port and allow the external legacy software to take control. This setting cannot be used with a Windows modem, or IP communications.

Note: When communicating through a modem, as soon as the communications port is released, the modem will hang up at the DTR drop. To make the modem insensitive to the DTR, use the AT command: AT &D0.

Hardware Flow Control: If the DavLink communications channel is slower than the Reach-Through communications port, Hardware Flow Control will ensure that no data will be lost. Hardware Flow Control must not be activated if the external equipment legacy software doesn’t support hardware flow control.

Configure your external equipment legacy software to use a second COM port in the computer, i.e. COMy in image below. As an example, if the legacy software is HyperTerminal, COM3 will be set as follows:

Equipment Legacy Software setup window (computer’s COMy serial port configuration)

Ensure that the baud rate for COMy (COM3 in image above) is set to the same value as for the COMx DavLink Serial Port Access in the Reach-Through Communications setup window (computer’s COMx). Other data parameter settings can be different according to the external legacy equipment. Refer to your legacy software documentation if other port settings are required.

Important: Users must ensure that every COM port is assigned a different Interrupt Request (IRQ) number. Otherwise, communications with external equipment will not work. To validate your IRQ settings using Windows XP, right-click the My Computer icon, select Properties, then the Hardware tab and click the Device Manager button. Look for ports, double-click the COM port (COMx, then COMy), select the Resources tab and verify the IRQ assigned to the port. If both COMx and COMy have the same IRQ number, we recommend you try a different COM port combination instead of changing the IRQ assignment.

Windows COM port settings (IRQ)

Finally, external equipment legacy software must not transmit modem commands if it uses a modem to access the COMy port because this will prevent proper communications.

Configuring the Davicom unit’s reach-through serial ports

To configure the Davicom’s reach through serial ports, click the Unit Configuration icon () then on the Devices tab select Serial Ports.

Davicom’s Reach-Through Serial Ports Configuration

To configure a specific reach-through serial port, select the port # (click the number) in the upper section of the dialog box set the following parameters in the lower part and then click Change.

Default Description: Long Unicode description for each of the Davicom reach-through serial ports. The description should include the external equipment to which the port is connected. (Maximum 30 alphanumerical Unicode characters). Refer to this article for more details.

Alternate Description: Short ASCII description for each of the Davicom reach-through serial ports. The description should include the external equipment to which the port is connected. (Maximum 18 alphanumerical ASCII characters).

Baud Rate: This number is the data rate used by the Davicom when communicating with the external equipment to which the reach-through serial port is connected.

Note: The baud rate setting for both the external equipment’s specific serial port and the Davicom’s rear-panel serial port must be the same, but the value doesn’t have to be identical to the legacy software baud rate setting.

Disable IP Encryption in MIP: Check this box to disable packet encryption during reach-through serial communications. This prevents data padding, normally used for data encryption, from adding unwanted delays that can hinder reach-through communications.

To configure another port, select the port # (click the number), set its parameters and then click Change.

To delete port settings, select the appropriate port # (click the number) and click Delete.

Once you are done with the configuration of the Davicom’s reach through serial ports, click OK. When asked if you wish to upgrade the Davicom’s memory, click Yes.

Communications parameters for the Davicom rear-panel serial ports are permanently set to: No parity, 8 data bits, and 2 stop bits.

These settings mean that the Davicom will transparently transfer 8 bits of data in both directions. This 8-bit data channel can also transmit 7-bit, odd-, even-, mark-, or space-parity data streams. Thus, it is not necessary for users to set the parity or number of bits for the rear-panel serial ports, and these parameters do not appear in Figure 44. However, users must set the external equipment’s specific serial port to have the same port settings as the external equipment legacy software. End-toend communications between the external equipment and its legacy software will transit via the Davicom’s 8-bit transparent data channel and transmitted data will not be affected.

Even though the Davicom transmits 2 stop bits, this is compatible with 1 and 2 stop-bit requirements. The extra stop bit only introduces a one-bit idle delay between two bytes of transferred data.

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