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7.3
Time-of-Day Synchronization
The SPC 4-2 supports two time-of-day synchronization mechanisms. The "En-
Clock-Sync" parameter bit (bit 6 in mode register 2) selects the required
mechanism.
If "En-Clock-Sync := 0" is set (status following reset), the SPC 4-2 behaves like the
SPC 4 in terms of time-of-day synchronization. Time-of-day synchronization is then
available only in the PA mode (XPB/PA = 1). In the PROFIBUS mode (XPB/PA =
0), the SM2-Time0/1 frames are filtered by the SPC 4-2. This mode should
therefore no longer be used.
If "En-Clock-Sync := 1" is set, the SPC 4-2 supports a time-of-day synchronization
mechanism that also permits the operation of several time masters. This
mechanism is available both in the PA mode and in the PROFIBUS mode.
The delay timer integrated in the SPC 4-2 has been extended to 24 bits (SPC 4: 16
bit delay timer). Each overrun of the integrated delay timer causes a "Del-Tim-
Overrun" interrupt (= bit 4 of the interrupt register) on the SPC 4-2 (as was also the
case on the SPC 4). This interrupt allows the user to extend the internal delay timer
as required.
To ensure compatibility with SPC 4, the delay timer of the SPC 4-2 is limited to 16
bits in the PA mode (XPB/PA = 1); in other words, the "Del-Tim-Overrun" interrupt
is generated when the 16-bit timer overruns.
In the PROFIBUS mode (XPB/PA = 0) the delay timer is 24 bits wide. The "Del-
Tim-Overrun" interrupt is generated when the 24-bit timer overruns. Bits 23 to 16 of
the delay timer can be read out at address 310H.
The time base of the delay timer is 32 us on the SPC 4. The "Factor-Delay-Timer-
Clock" parameter register determines the dividing factor for the delay timer. This
allows any other time base to be set. To achieve a higher resolution in time-of-day
synchronization, a time base of 1 us as well as 32 us is in discussion. The following
dividing factors must then be set:
Quartz
48 MHz
20 MHz
2 MHz
48 MHz
20 MHz
2 MHz
84
Fakt-Del-CLK
Resolution
1535
32 us
639
32 us
63
32 us
47
1 us
19
1 us
1
1 us
PROFIBUS Controller SPC 4®-2 LF
C79000-G8976-C157-3
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