SRTP - Service Request Transfer Protocol

See also: Ethernet Configuration Overview

 

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SRTP Overview

Service Request Transfer Protocol (SRTP) is a GE Fanuc Automation protocol, which allows a remote SRTP Client to request services from an SRTP Server. In this context, the OCS acts as an SRTP Server, which responds to requests from one or more SRTP Clients. Since SRTP was originally designed to support services provided by GE Fanuc Series 90 PLC products, the OCS’s SRTP protocol, for OCS and RCS products, does not support all possible SRTP services. The OCS’s implementation of SRTP is mainly limited to those services required for the exchange of PLC register data.

Note: This is a Built-In (Resident) Industrial Protocol.

The following SRTP service requests are supported:

SRTP Service Requests
Request Code Service Name
0 PLC_SSTAT
1 PLC_LSTAT
4 READ_SMEM
7 WRITE_SMEM
33 CHG_PRIV_LEVEL
67 RET_CONFIG_INFO
79 SESSION_CONTROL
97 PLC_FEATURES_SUPP

The READ_SMEM and WRITE_SMEM requests are supported for the following register types:

SRTP Register Types
Selector Register Type
8 %RClosed Retentive 16-bit registers. 16 bit
10 %AIClosed 16-bit input registers used to gather analog input data such as voltages, temperatures, and speed settings coming from an attached device. 16 bit
12 %AQClosed 16-bit output registers used to send analog information such a voltages, levels, or speed settings to an attached device. 16 bit
16 %IClosed Single-bit input registers. Typically, an external switch is connected to the registers. 8 bit
18 %QClosed Single-bit output registers. Typically, these bits are connected to an actuator, indicator light or other physical outputs. 8 bit
20 %TClosed Non-retentive single-bit registers. 8 bit
22 %MClosed Retentive single-bit registers. 8 bit
30 %SClosed Single-bit bit coils predefined for system use. 8 bit
70 %I 1 bit
72 %Q 1 bit
74 %T 1 bit
76 %M 1 bit
84 %S 1 bit

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SRTP Configuration

If SRTP protocol will be used in the application, the general OCS Configuration, previously described in the [General Configuration Chapter], must be performed, and SRTP must be enabled. To enable SRTP protocol, use Cscape Programming Software, to perform the following two steps:

  1. Open the OCS configuration dialog (Home > Controller > Hardware Configuration > LAN1 / Config) as described in Ethernet Configuration Overview

  2. Enable SRTP by checking the SRTP Slave (90-30 Service Request) checkbox in the Module Configuration dialog, see below.

No additional configuration is required for SRTP protocol, so the Configure Selected Protocol button is disabled. If SRTP is enabled and the OCS has been assigned an IP Address and Net Mask, then it will respond to service requests from an SRTP Client.

 

SRTP Operation

With respect to SRTP protocol, the OCS’s behavior depends on whether the OCS is in RUN mode or not.

  • When the OCS is in RUN mode, the OCS responds normally to SRTP Client requests.

  • When the OCS is not in RUN mode, it still responds to SRTP Client requests, with the following differences:

    • When a WRITE_SMEM request is received from an SRTP Client, to write a block of OCS registers, a reply is sent to the client, but the data is not written to OCS registers.

    • When a READ_SMEM request is received from an SRTP Client, to read a block of OCS registers, a reply is sent to the client, but the data returned to the client is the last known values of the requested OCS registers, and is not actually read from the OCS registers.

    • For all requests received from an SRTP Client, the reply will indicate to the client that the OCS is not in RUN mode, by returning the RUN DISABLED code in the Piggyback Status word.

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