# BASEstartm Classic DAS
for Modicon®
Programmable Controllers
Installation and User's Guide

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## 2.3.4 Setting DAS-Specific Parameters

The following sections describe how to set the DAS-specific BASEstar Classic parameters.

None of the parameters created for the DAS for Modicon programmable controllers are dynamic. BASEstar Classic device connection management must be shut down and started again before parameter modifications become effective.

### 2.3.4.1 Setting Modbus Parameters

The installation procedure for the DAS for Modicon programmable controllers creates BASEstar Classic parameter(s) to allow you to tune the DAS environment for your Modbus network. These parameter(s) are listed in Table 2-10.

Table 2-10 Modbus Parameters
Parameter | Default | Description
--- | --- | ---
ILAN$MODBUS_TRANSMIT_DELAY | 0 00:00:00.00 1 | This value specifies the time to delay after receiving a response to a Modbus message before sending the next message to a new address.

1The value of this parameter is dependent on the baud rate and should be set to at least three and one-half character times. The lowest value that this parameter can be set to is 00:00:00.01 which is an acceptable value for baud rates of 4800 baud and higher.

Modbus requires an inter-message delay and on fast systems, normal processing overhead does not provide enough delay resulting in intermittent timeouts. This problem is most likely to occur on systems with directly connected ports (not LAT). The ILAN$MODBUS_TRANSMIT_DELAY parameter provides this delay if the parameter is not set to 0 (the default).

### 2.3.4.2 Setting Unsolicited Parameters

The installation procedure for the DAS for Modicon programmable controllers creates BASEstar Classic parameters to allow you to tune the DAS environment for collecting unsolicited data. These parameters are listed in Table 2-11.

Table 2-11 Unsolicited Parameters
Parameter | Default | Description
--- | --- | ---
ILAN$MOD984_MAX_REG_ADDRESS 1 | 1000 | This value specifies the maximum holding register offset value that can be specified as the destination in a Modbus MSTR write function block.
ILAN$MOD984_UNSOL_QUEUE_SIZE 1 | 7 | This value specifies the size of the queue to receive unsolicited write messages from the Modbus-Plus or TCP/IP network. A larger value allows more data to be handled in a burst of messages from the Modbus-Plus or TCP/IP network at the expense of more memory consumption.
ILAN$MODHOST_MAX_REG_ADDRESS 2 | 1000 | This value specifies the maximum holding register offset value that can be specified as the destination in a Modbus MSTR read function block.
ILAN$MODHOST_UNSOL_QUEUE_SIZE 2 | 7 | This value specifies the size of the queue to receive unsolicited read messages from the Modbus-Plus network. A larger value allows more data to be handled in a burst of messages from the Modbus-Plus network at the expense of more memory consumption.
ILAN$MODHOST_UNSOL_WRITE 2 | 0 | This value specifies whether unsolicited writes are sent to the MODHOST device or to the device identified by the first five words of the message. If this parameter is "0", then routing information is expected to be in the first five words of the message and the write is sent to the device with a matching network address.

1Modbus Plus or TCP/IP networks.
2Modbus Plus networks only.
3Modbus networks only.

### 2.3.4.3 Setting TCP/IP Parameters

The installation procedure for the DAS for Modicon programmable controllers creates BASEstar Classic parameters to allow you to tune the TCP/IP environment. These parameters are listed in Table 2-12.

Table 2-12 TCP/IP Parameters
Parameter | Default | Description
--- | --- | ---
ILAN$MODTCP_PROBE_TIME 1 | 10 | This value specifies the time in seconds that TCP/IP will use to probe a for a broken connection.
ILAN$MODTCP_DROP_TIME 2 | 30 | This value specifies the time in seconds after a broken connection has been detected until the connection is actually dropped.

1The probe time plus drop time is the total time that will elapse between when a connection is physically broken until the DAS will detect that the connection no longer exists.
2The drop time must be greater than the probe time or a bad parameter error will be returned when trying to set the socket option. The drop time should be an even multiple of the probe time.

For information on configuring and setting up Digital TCP/IP Services for OpenVMS see Digital TCP/IP Services for OpenVMS Installation and Configuration.

## 2.3.5 Setting Up Plant-Floor Equipment

For information on configuring your Modicon equipment, see Appendix A. For information on your specific device, refer to the Modbus System Planning Guide and the J478 Stand-Alone Modem Guide for Modbus communications, to the Modicon DEC Host Based Devices User's Guide for Modbus-Plus communications or to the Modicon Quantum Ethernet TCP/IP Module User Guide for Modbus TCP/IP communications.

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