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8 DTU3005P Profibus Application Notes

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The procedure that the Profibus host must follow to

issue commands through the output data word is as

follows:

1. Set the command number word to 0, which tells

the DTU3005P that the command data is not

valid or no command is currently requested.

2. Set the Device Number, Device Type Code, and

Data Value to the appropriate values.

3. Set the Command Number to the appropriate

value.

The DTU3005P processes only the command one

time after any word of the output data is changed.

By setting the Command Number to 0 while chang-

ing any other words in the output data, no undesired

commands are processed.

Most commands issued by the Profibus host will

result in feedback in the real-time data so the host

should know when the command is received by the

DTU3005P and it is safe to change the output data

to issue a new command.

8.7 Input Data to Host Transfer

Method

When only one device is configured, that device's

real-time data is continually transferred to the Profi-

bus-DP host. When multiple devices are configured,

there are two ways that the DTU3005P can be con-

figured to alternate between sending the data for

each device.

Method 1

The first method is to specify a delay time. The

DTU3005P can be configured to send Device 0's

data until the delay time has expired then it automat-

ically switches over to send Device 1's data for the

same time period. It repeats this process in Device

number order for each device in the list of config-

ured devices. When the last device's data has been

sent and the delay time has expired, the DTU3005P

begins sending Device 0's data again.

Method 2

The second method requires the use of the output

data (4 output words) that are transferred from the

Profibus-DP host to the DTU3005P. A command

number of 255 is used to request the device’s real-

time data the Profibus host wants to receive. When

command number 255 is received in the third word

of the output data, the DTU3005P begins sending

the real-time data for the device number and device

type specified in the first and second words of the

output data (see Tabl e 8.5). It will continue sending

the data for that device until another command num-

ber 255 is received to switch to a different device.

This process allows the Profibus host to tell the

DTU3005P when it has received the latest real-time

data for one device and is ready for data from the

next device. The Profibus host will leave the output

data set until it has received the requested device's

data to verify that the DTU3005P has received the

request to switch to a particular device.

8.8 DTU3005P Diagnostic Data

A total of 24 bytes of Diagnostics Information is sent

to the Profibus-DP host. See Tab le 8 . 6 for the for-

mat for these bytes.

Word 2: Command Number

Specifies the command to perform. Command

numbers are different for each type of device and

can be found in the Device Command Data

Received from PLC section for each device in

Appendix C.

Word 3: Data Value

Data required for the command as shown in

Appendix C. Some commands do not require any

data values. In this case, the value of this word is

ignored.

Table 8.5 Profibus-DP Word Format

Table 8.6 Byte Format Sent to Profibus-DP Host

Byte 0: Station Status_1