Siemens SPC3 manual UserWatchdogTimer, GlobalControl SAP58

01 Din_Buf_Ptr1

10 Din_Buf_Ptr2

11 Din_Buf_Ptr3

Figure 6.13: Din_Buffer Management

When reading the ‘New_Din_Buffer_Cmd’ the user getsthe information which buffer (U-buffer) belongs to the user after the change (Din_Buf_Ptr 1-3).

Figure 6.14: Next_Din_Buffer_Cmd

6.2.5.3 User_Watchdog_Timer

After power-up (‘DATA_EX’ state), it is possible that SPC3 continually answers Write_Read_Data-telegrams without the user fetching the received Din buffers or making new Dout buffers available. If the user processor ‘hangs up,’ the master would not receivethis information. Therefore, a ‘User_Watchdog_Timer’ is implemented in SPC3.

This User_Wd_Timer is an internal 16-bit RAM cell that is started from a ‘R_User_Wd_Value15..0’ value the user parameterizes and is decremented with each received Write_Read_Data telegram from SPC3. If the timer attains the ‘0000hex’ value, SPC3 transitionsto the ‘Wait_Prm’ state, and the DP_SM carries outa ‘Leave_Master.’ The user must cyclically set thistimer to its start value. Therefore, ‘Res_User_Wd= 1’ must be set in mode register 1. Upon receipt of the next Write_Read_Data telegram, SPC3 again loads the User_Wd_Timer to the parameterized value ‘R_User_Wd_Value15..0’ 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 even set at its parameterized value.

6.2.6 Global_Control (SAP58)

SPC3 itself processes the Global_Control-Telegrams in the manner already described. In addition, this information is available to the user.

The first byte of a valid Global_Control command is stored in the R_GC_Comand RAM cell. The second telegram byte (Group_Select) is processed internally.