Материал: m013802e_b

5.2 Controller

750-812,

750-814,

750-815,

750-816

5.2.1 Settings

As opposed to the MODBUS coupler the factory configuration of the controller change is not made by DIP switch, but is changed using a PC. The communication between the controller and PC is described in the ‘Start-up and diagnosis’ chapter.

The controller is set on the software side using the ‘Fieldbus configuration’ function block of the WAGO-I/O-PRO library. If this module is taken up in the control program, the setting is made automatically even after changing the controller. The settings are taken over into the controller parameter block. If the desired values are not already set, a firmware reset is automatically made in bus operation and the controller restarts with the selected settings.

If the controller is to be set independent of a machine or plant, a program which only comprises of the configuration module can be downloaded and started from the programming system.

Fig. 5.5: Function block for controller setting

The coupler settings are described as follows. Here the term ‘Frame’ is frequently used. ‘Frame’ is a data transfer record.

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5.2.1.1 Standard settings

The controller is delivered with the following standard values:

Table 5.12: Standard settings, controller

5.2.1.2 Baud rate setting

The following baud rates can be set:

Table 5.13: Baud rates, controller

The standard default setting is 9600 Baud.

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5.2.1.3 Error detection, length of the character string

A parity bit can additionally be transmitted with each byte. Data transfer faults can be recognised with the help of the parity bit. A differentiation is made between parity checks for even parity, odd parity and no parity.

For this the number of set bits (=1) are counted in the transmitted data bytes. For example, during the transmission of the character string 1100 0101 the number of set bits is even, namely 4. If the setting of an even parity bit is selected, then in this case it is set to 0, so that the number of set bits still remains even. Analog to this, the odd parity bit 1 would be selected so that the number of set bits will be odd.

This type of error detection is assured for one error, for several errors under certain circumstances this error detection may no longer be assured. If the coupler recognises a parity error, the frame is ignored and a new frame can only be received following a renewed ‘Start of Frame’.

If the slave receives faulty frames, these will not be replied to. The master detects this error in that after the preset time (Time-out) no corresponding frame is received.

In the MODBUS coupler 750-812 a parity bit can be attached to each byte. The data length selected can be 7 or 8 bit. In addition it is possible to add 1 to 3 stop bits.

Table 5.14: Byte Frame, Controller

The standard setting is no parity, 8 bit data length and 1 stop bit. This setting is ignored when transferring data in RTU mode, as the format of this mode is set to 8 bit.

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5.2.1.4 End of Frame Time

The end of frame time is the pause time following a frame which is required to switch over the repeater in slave. This time must permit gaps during a frame without resulting in a faulty detection of the end of frame time.

The setting of the end of frame time is made with the input ENDOFFRAMETIME.

Table 5.15: End of Frame Time, Controller

The standard setting is 3 x frame time.

5.2.1.5 ASCII/RTU mode

MODBUS permits two different transmission modes:

The setting is made using input ASCIIRTUMODE.

Table 5.16: ASCII-/RTU mode, controller

The standard setting is RTU mode.

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5.2.1.6 Error Check

A check sum (CRC) is calculated from the frame to be transmitted in the sender (higher ranking controls). This check sum is transmitted in the frame to the receiver (controller). Once the error check is activated, this check sum is compared with the check sum calculated in the coupler on the basis of the same instruction. An error is signalled by a red LED ‘CRC’.

The setting is made via the input ERRORCHECKING.

Table 5.17: Error Check, controller

Error Check activated is the standard setting.

5.2.1.7 Extended Functions

The registers for further internal diagnostic possibilities (extended functions) in the address space of the coupler are not yet available. For this reason set the attendant input

EXTENDEDFUNCTIONS to FALSE.

Extended EXTENDEDFUNCTIONS

Functions

Value

without FALSE

available TRUE

Table 5.18: Extended functions, controller

In the standard setting, other diagnosis possibilities are switched off.

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