Freescale Semiconductor MC9S12ZVM series, Справочное руководство

Страница: 479 / 825

Chapter 13 Programmable Trigger Unit (PTUV2)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor 479
The trigger generation of the PTU module is synchronized to the incoming reload event. This reload event
resets and restarts the internal time base counter and makes sure that the first trigger value from the actual
trigger list is loaded. Furthermore the corresponding module is informed that a new control cycle has
started.
If the counter value matches the current trigger value then a trigger event is generated. In this way, the
reload event is delayed by the number of bus clock cycles defined by the current trigger value. After this,
a new trigger value is loaded from the memory and the TG waits for the next match. So up to 32 trigger
events per control cycle can be generated. If the trigger value is 0x0000 or 32 trigger events have been
generated during this control cycle, the TGxDIF bit is set and the TG waits for the next reload event.
Figure 13-22 shows an example of the trigger generation using the trigger values shown in Figure 13-23 .
Figure 13-22. TG0 trigger generation example
NOTE
If the trigger list contains less than 32 trigger values a delay between the
generation of the last trigger and the assertion of the done interrupt flag will
be visible. During this time the PTU loads the next trigger value from the
memory to evaluate the EOL symbol.
t
Delay T0
Delay T1
Delay T2
Control Cycle
PTUCNT
TG0LIST
TG0TNUM
0
1
2
3
0
T0 T1
T2
0x0000
TG0DIF
T0
outgoing trigger events
TG0TV
reload event
reload event