Siemens SIMATIC NET SPC 4-2 LF, Manual

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PROFIBUS Controller SPC 4®-2 LF
104
C79000-G8976-C157-3
The timeout timer (9-bit) is a one-shot-timer that increments at the slot interval rate
(TO
CLK
). The controller takes the XSlot/Syni status bit. If the Syni-timer is running
(XSlot/Syni = 1), the timeout timer is locked. With the change from Syni to Slot
(XSlot/Syni = 0), the timeout timer is cleared, enabled, and incremented at each
TOCLK (slot interval). If there is activity again on the serial bus before the timeout
timer elapses (XSlot/Syni = 1), the controller stops the timer again.
When the timer elapses, the timeout status flag is set and the timer is stopped.
RxD/XRxA
XSlot/Syni
T
ID
Load TOT 0
TOCLK
Timeout
T
Timeout
TIMEOUT stop TIMEOUT START TIMEOUT elapsed
Figure 7-28 Control of the Timeout Timer
7.11.6 New Timers in the FF Mode
Description
The SPC 4-2 contains 4 new 16-bit timers. These can be used only in the FF mode
since they use interrupt bits that are only free in the FF mode. They all run at the
baud rate speed.
In the timer type register, the user can set the timers either as "one-shot" or as
"cyclic" timers.
The timers are started, stopped, and resumed using the new timer control register.
A timer can only be started when its start value has been entered in the timer
register. When it starts, each timer loads the start value from its start value register
and counts down until it reaches the value 0. It then triggers an interrupt. The
"cyclic" timer then goes back to its start value immediately and starts counting
again, while the "one-shot" timer remains at 0.