Figure 6-15: Coding of New_Din_Buf_Cmd
User_Watchdog_Timer
After start-up (DATA-EXCH state), it is possible that the VPC3+S
continually answers Data_Exchange telegrams without the user fetching
the received Dout-Buffers or making new Din-Buffers available. If the user
processor ‘hangs up' the DP-Master would not receive this information.
Therefore, a User_Watchdog_Timer is implemented in the VPC3+S.
This User_WD_Timer is an internal 16-bit RAM cell that is started from a
user parameterized value R_User_WD_Value and is decremented by the
VPC3+S with each received Data_Exchange telegram. If the timer reaches
the value 0000H, the VPC3+S goes to the WAIT-PRM state and the
DP_SM carries out a LEAVE-MASTER. The user must cyclically set this
timer to its start value. Therefore, ‘Res_User_WD = 1’ must be set in Mode
Register 1. Upon receipt of the next Data_Exchange telegram, the VPC3+S
again loads the User_WD_Timer to the parameterized value
R_User_WD_Value and sets ‘Res_User_WD = 0’ (Mode Register 1).
During power-up, the user must also set ‘Res_User_WD = 1’, so that the
User_WD_Timer is set to its parameterized value.
6.2.6 Global_Control (SAP 58)
The VPC3+S processes the Global_Control telegrams like already
described.
The first byte of a valid Global_Control is stored in the R_GC_Command
RAM cell. The second telegram byte (Group_Select) is processed
internally.
The interrupt behavior regarding to the reception of a Global_Control
telegram can be configured via bit 8 of Mode Register 2. The VPC3+S
either generates the New_GC_Control interrupt after each receipt of a
Global_Control telegram (default) or just in case if the Global_Control
differs from the previous one.
The R_GC_Command RAM cell is not initialized by the VPC3+S. Therefore
the cell has to be preset with 00H during power-up. The user can read and
evaluate this cell.
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