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DPC31 HW

Page 32 Version V 1.0

DPC31 HW Description

Byte Control_Command:

Bit 7, 6, 0: Reserved

The designation “Reserved” indicates that these bits are reserved for future

function expansions. If such a bit is set, DPS sets ’Diag.Not_Supported=1’, and the

“Leave_Master macro’ is executed. However, if the user parameterizes

‘Check_No_GC_Reserved=1’ in the param register, the Reserved bits are not

checked.

Bit 5: Sync

The output data transferred with a Write_Read_Data message is changed from ‘D’

to ‘N’ (DX_OUT interrupt is generated). The subsequently transferred output data

is kept in ‘D’ until the next ‘Sync’ command is made. The same reaction occurs for

‘Sync_Supported=0’ as does for a set Reserved bit.

Bit 4: Unsync

The command ‘Unsync’ cancels the ‘Sync’ command. In addition, as in the case of

‘Sync’, the previously transferred output data is changed from ‘D’ to “N’.

Bit 3: Freeze

The input data is fetched from ‘N’ to ‘D’, and “frozen”. New input data will be

fetched only if the master sends the next ‘Freeze’ command. The same reaction

occurs for ‘Freeze_Supported=0’ as does for a set Reserved bit.

Bit 2: Unfreeze

With ‘Unfreeze’, freezing the input data is cancelled. In addition, as in the case of

‘Freeze’, new input data that was made available is fetched from ‘N’ to ‘D’.

Bit 1: Clear_Data

With this command, the Dout buffer is not deleted and it is not changed; rather, the

mode ‘N_Cl=1’ is set in the Dout_Buffer_ SM, and the user interrupt ‘DX_OUT’ is

generated. If the user then fetches his new Dout data, the C and U buffers are

exchanged and the user gets the message ‘U_Buffer_Cleared’.

With ‘sync’, data buffers are made available synchronously. However, this does not provide for synchronous

mapping directly to the I/O as is the case with the LSPM2. Although the application is interrupted via the

‘DX_OUT interrupt’, the transfer time from the buffer that was made available to the I/O is subject to interrupt

latency. To bypass it, the interrupt ‘DX_OUT’ can directly be applied to the port PB

if a global control

message is received with ‘Sync’, provided ‘Enable DX_OUT_Port=1’ was parameterized in the C31_Control

transfer from the buffer to the I/O in a fixed time reference.

With ‘Freeze’, the available Din buffer in ‘N’ is frozen to ‘D’. Thus, in distinction to the LSPM2, no updating is

provided at this time from the I/O. To circumvent this, the user would have to make the input data, if it

changes, available immediately in the N buffer (high processor capacity required).

For each valid Global_Control message, the Control_Command byte is stored in the RAM cell

‘GC_Command’. At initialization, DPS preassigns FFh (not a valid value) to the RAM cell ‘GC_Command’.

The user can read and interpret this cell. Depending on the setting of ‘New_GC_Int mode’ (refer to Param

generated only if the Control_Command byte for the last received Global_Control message has changed.

With ‘New_GC_Int mode=1’, the interrupt is generated after each receipt of a GC message.

Failsafe Mode:

To support the failsafe mode, a ‘Spec_Clear_Mode’ is implemented in the DPC31. The master generates

such a Clear mode by sending a Global_Control message with ‘Clear_Data=1’. The Din data has to continue

to be fetched during this Clear_Mode. For this, the master has to send the Write_Read_Data message with

the parameterized number of Dout data bytes=00h. However, in the case of many slave applications, the

value 00h does not correspond to the Clear mode (for example, substitute values for analog modules). Here,

the user generates the corresponding substitute values. If the Global_Control message was not received

because of a bus fault, this slave does not know that it should be in the Clear mode; therefore, the

subsequently received Dout data bytes with the value 00h can’t be replaced with the substitute values.

To support the failsafe mode, the DPC31 also accepts Write_Read_Data messages without output data even

though the parameterized Dout length ‘Dout_Buffer length # 0’ is set. After the receipt of this message, the C

buffer where the substitute values are stored, is then included in the buffer cycle. If the user fetches this

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Siemens SPC3 Specifiche Pagina 34

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