Rockwell Automation T3837 User Manual

ICS Regent

Important!

PD-6048

MODBUS Master Package

for

MODBUS Master Function Block

The MODBUS Master package for W package which allows the user to MODBUS Master function blocks for Regent application programs. W seamlessly integrated with the base WINTERPRET

MODBUS Master function blocks allow the Regent to use devices which respond to MODBUS commands to collect and disseminate data for non safety-related application.

hen installed on the PC, the package is

INTERPRET

(T3837)

Issue 1, August, 96

is an add-in software

software.

Software Installation

The MODBUS Master package is installed on the PC running the W

INTERPRET application software. The WINTERPRET

provides the necessary installation software to install this add-in package. The package should be install the W

INTERPRET

Installation Procedure

The files on the MODBUS Master package diskette are in compressed form. You cannot simply copy the files to your hard drive — they must be decompressed before they will run. You must have the W package distribution disk in order to run the setup procedure to install the MODBUS Master package.

To install the MODBUS Master package, use the following sequence:

Insert the WINTERPRET base package distribution disk into drive A: or B:

Start Windows (if it isn’t already running).

Choose Run from the Program Manager’s File menu.

base package.

base package

ed at the same time or after you have installed

INTERPRET

base

Industrial Control Services

(Issue 1)

MODBUS Master Package for

4. Type a:\ base package disk in drive B: type b:\ press ENTER.

5. In the WINTERPRET which you have installed the W that you have already installed W

6. In t Master package box.

7. Choose

When the installation is completed, you can run the WINTERPRET application and create MODBUS Master function blocks in your application programs.

he W

setup.exe

INTERPRET

in the text box. (if you inserted the WINTERPRET

Setup dialog box enter the name of the directory in

Installation dialog box check the MODBUS

to have the setup program install the package software.

INTERPRET

setup.exe

INTERPRET

(T3837)

.) Choose OK or

base package (This assumes

). Choose

Continue.

Working with MODBUS Master Function Blocks

MODBUS Master function blocks are created as part of an application program which may also contain other types of function blocks. A single application program is made up of as many as 50 function blocks of any type or combination.

When you installed the MODBUS Master package, additional software was added to W function blocks. With this additional software you can create MODBUS Master function blocks by opening a project, opening a program, and opening (or creating) a function block.

The code generated by W (MODBUS Master function block code) responds to control signals, prepares MODBUS commands to be sent, decodes received MODBUS responses, and in general performs the operations that are associated with a MODBUS Master.

The MODBUS Master code is executed in the Regent in the same manner as any other function block code. It is called once per application scan as long as the program to which the MODBUS Master function block belongs is in the run state. Instead of performing a complete MODBUS scan each

INTERPRET

to allow you to work with MODBUS Master

for the MODBUS Master

PD-6048 August, 96

(Issue 1)

MODBUS Master Package for

time it is called, the MODBUS Master function block code splits up the tasks so that it can be done a

a time. This allows the Regent system to remain responsive, as well as eliminating the potential loss of time while waiting for MODBUS responses.

For an overview about Regent application programs and function blocks and how to create them using W

with Programs and Function Blocks

little at

INTERPRET

, refer to Section 5,

, in the Regent User’s Guide.

(T3837)

Working

Using MODBUS Master Function Blocks

The MODBUS Master function block allows the user to specify the following Regent variables:

Variables to receive data from MODBUS slaves

Variables to be the source of data sent to MODBUS slaves

Variables to serve as control signals for the function block

Variables to receive the current status and other information about the function block.

Each Regent variable used to send or receive data may be associated with a different MODBUS node and address. The user may specify which port on the Regent to use, including the s configuration.

The MODBUS Master function block compiler may be invoked from the File menu in the MODBUS function block editor when the editor is closed and the changes have been saved for the current function block. The compiler translates the user’s inputs from the source file into an object file to be loaded into and executed in the Regent.

The compiler has two separate phases: registration and generation. In the registration phase, the compiler registers t from the project dictionary. The generation phase consists of parameter validation followed by code and data segments generation. The registration phase follows the conventions (and requirements) imposed by other W

INTERPRET

each function block compiler, and is where MODBUS-Master-specific code is introduced.

function block compilers. The generation phase is unique to

election of a secondary port for a dual-link

ag names and retrieves definitions

PD-6048 August, 96

(Issue 1)

MODBUS Master Package for

Name

Size Type

Description

NABLE

Coil Input

Enables execution of the function block. Energize to execute the function block.

RROR

Coil

Output

Enunciates a MODBUS function block error. Energized when an error occurs.

ESET

Coil Input

Resets the error information. Energize to reset the information. While energized, no errors w

ill be

reported. N

ODE

Word

Output

The MODBUS node associated with the error. 0 when there is no error.

ODE

Word

Output

The MODBUS function block error code. 0 when there is no error.

IME

Float

Output

The time it took to complete the last MODBUS scan in ms. 0 until a scan has been completed.

OGGLE

Coil

Output

This control signal changes state at the beginning of each MODBUS scan. (Its period it typically 2 *

Time)

INTERPRET

(T3837)

Operation

The MODBUS function block uses control signals to report information and accept runtime control used like normal Regent variables. Table 1 identifies these control signals.

Table 1 - Control Signals

NABLE

NABLE is de

and all other signals are invalid (exception: the RESET honored).

RROR

enunciates any errors that the MODBUS function block code

encounters.

ODE

and

when

RROR is active. NODE

a zero [0] indicating the MODBUS master itself). specific MODBUS exception code.

The

OGGLE

the initial scan, T

OGGLE

desired instead of a toggle, external application code (in the same program) may reset

directives. The signals are user defined, and may be

controls the execution of the function block at runtime. When

ener

gized (OFF), the function block code is not executed

input signal will still be

ODE

are used to further define an error. They are valid only

contains the MODBUS node that is in error (

ODE contains the

state changes each time a MODBUS

IME

contains the length (in ms) of the MODBUS scan.

is initialized to de-energized (OFF) for the initial scan. If a pulse is

OGGLE

to the de-energized state after a rising edge is detected.

scan is completed. After

PD-6048 August, 96

(Issue 1)

MODBUS Master Package for

Field Size

Description

Node Byte

The MODBUS node to broadcast this command to. Function

Byte

The MODBUS function to broadcast. Address

Word

The starting MODBUS address for this command. Count

Word

The number of MODBUS variables to be returned. CRC Word

The pre-calculated CRC for the MODBUS command. Offset

Word

The index into the Read Var table for the initial MODBUS variable.

Reserved

Word

Reserved for internal use.

Field Size

Description

Value

Word

The value of the regent varia

ble.

Note:

INTERPRET

(T3837)

Tables define the work that the MODBUS function block performs. The primary table used is the ‘Read Command’ (RC) table. Each entry in the RC table is eight bytes wide, with the first six bytes corresponding exactly to the same fields in a MODBUS command. Each entry (starting with the first) in the RC table sends a MODBUS command. When the response is received, the Count field is used to decode the received data. The Index field, in conjunction with the Read Variable table, is used to store the data in its proper place. Tables 2 and 3 define the Read Command and Read Variable Tables, respectively.

Table 2 - Read Command Table

Table 3 - Read Variable Table

When each entry in the Read Command table has been sent, the function block code waits for all the replies to be returned. When all of the replies have been received and processed, a single MODBUS scan has been completed. At the start of the next MODBUS scan, the entire process starts over at the beginning of the RC table.

Abstractly, the RC table can be thought of as a “Read” queue. This queue is replenished at the start of each MODBUS scan, and is empty at the scan’s completion. Future pseu queue as the READQ.

PD-6048 August, 96

(Issue 1)

do code examples refer to the abstract RC table

MODBUS Master Package for

Field Size

Description

Node Byte

The MODBUS node to notify when the v

alue changes.

Function

Byte

The MODBUS function to use for notification. MODBUS

Address

Word

The MODBUS address to use for notification.

Value

Word

The current value of the variable. CRC Word

Placeholder for the run-time calculated CRC of the MODBUS command.

Last Value

Word

The last known value of the variable. Reserved

Word

Reserved for internal use.

Note:

INTERPRET

(T3837)

The ‘Write Command’ (WC) table is also used by the MODBUS master function block code. In many ways, the WC table is similar to the RC table. However, the WC table does not utilize a corresponding Write Variable table because each “Write” only references a single variable. Table 4 defines the Write Command Table.

Table 4 - Write Command Table

Every application scan the function block code is executed, each variable defined in the WC table is examined by comparing its current value to the co

ntents of the Last Value field. If the two value differ, the Send Flag field is

set and the current value is copied into the Last Value field.

Each entry in the WC table, with the Send Flag set, causes a MODBUS command to be sent. When the response is received, the Send Flag for that variable is cleared. For the initial MODBUS scan, the Send Flag field is set for every entry in the table. The WC table is processed from the initial entry to the final entry in sequence. If no more MODBUS commands can be sen

t, WC processing stops and resumes again on the same entry the next

time the function block code is executed.

PD-6048 August, 96

Abstractly, the WC table can be thought of as a “Write” queue. This queue is full for the initial MODBUS scan. Future pseudo code example refer to the abstract WC table queue as the WRITEQ.

The tasks performed each time the function block code is executed are as follows:

· ENABLE

is checked to see if the function block should be executed. A check is made to see if this is the initial MODBUS scan. If so, local variables and tables are initialized.

(Issue 1)

MODBUS Master Package for

A check is made to see if this is the start of a MODBUS scan. If so, the ‘MODBUS Scan Time’ timer is reset.

Each “Write” variable is check to see if it has changed state (or value), and those that have are added to the WRITEQ.

Outgoing packets are sent.

While !FULL(SENDQ)

If !EMPTY

(WRITWQ)

ENQ(SENDQ, DEQ(WRITWQ))

Else If !EMPTY(READQ)

ENQ(SENDQ, DEQ(READQ))

End If

End While

Incoming responses are received, and the appropriate actions are taken.

While !EMPTY(RECVQ)

PROCESS(DEQ(RECVQ))

End While

A check is made to see if this is the end of the MODBUS scan. If so, copy the timer and toggle the toggle.

RESET

is checked to see if the error signals should be cleared. This

occurs even if the function block is not executed.

INTERPRET

(T3837)

The MODBUS function block code keeps track of how many me

ssages are outstanding by incrementing a counter for each ENQ(SENDQ, DEQ(READQ)), and decrementing the same counter for each DEQ(RECVQ) when the response is a “Read” response. A MODBUS scan is considered complete when the counter is zero (0) and the READQ is empty (COUNT == 0 && EMPTY(READQ)).

At the beginning of each MODBUS scan, a copy of the system millisecond timer is made. At the completion of a MODBUS scan, this value is copied into the T

IME

variable and the

OGGLE

signal is inverted.

Placing a MODB

US command on the SENDQ involves copying the MODBUS command to a buffer, generating the appropriate error-check code, and sending the command to the correct port (primary or secondary). Internal variables are used to determine the port.

If a secondary port was defined, once each MODBUS scan the initial MODBUS ‘Read Command’ for each node is sent via the secondary port. The result of this command is ignored, it is used only to check for a valid connection. The MODBUS Node table is used to track the status o node’s response. Table 5 defines the MODBUS Node Table.

f each

PD-6048 August, 96

(Issue 1)

+ 16 hidden pages