EM6812F2TP24B datasheet(54/81 Pages) EMMICRO

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13.2.3 Start control system

There are two principal ways to start the counter:

•

Internal start:

−

Software writing the SWStart bit.

•

External signals on port A input:

−

State condition: External start on input state (down-counting while condition true)

−

Pulse condition: External start on input pulse, stop on next pulse.

•

The selection of the start source and the corresponding port A input is done in register RegTimXCfg bits StartXSel[2:0].

•

CPU controlled software Start or State / Pulse Start condition in case of external start is defined in registers

RegTimersStart.

•

The SwStartX bits can be used as busy flags in case of software start. If the timer is started by port A input conditions,

the SwStartX bits will remain ‘0’, busy information can be derived from reading the timers status value or by detecting

the start / stop conditions.

Each timer has 8 different start sources. Software start is selected by default, activated by writing bit SWStartX in register

RegTimersStart. The selection of other start sources is done with StartXSel[2:0] in RegTimXCfg.

Table 48. Start selection

Timer1

Timer2

Timer3

Timer4

StartXSel[2:0]

Selection with

Start1Sel[2:0]

Selection

with

Start2Sel[2:0]

Selection

with

Start3Sel[2:0]

Selection

with

Start4Sel[2:0]

000

Soft

start

SwStart1

Software

with

SwStart2

Software

with

SwStart3

Software

with

SwStart4

001

Ext. start PA1

Ext. start PA0

010

Ext. start PA2

Ext. start PA1

011

Ext. start PA3

Ext. start PA2

100

Ext. start PA4

101

Ext. start PA5

110

Ext. start PA6

111

Ext. start PA7

Start selection must not be changed while the timer is running.

13.2.3.1 Software Start Condition

In Software start, the CPU writes the start condition SWStartX=’1’. The software start gets synchronized on the next falling

edge of the selected counter clock. The positive edge synchronization signal then enables the counter function.

The counter is stopped by either writing the SWStartX=’0’ or on Zero-Stop mode when the counter value reaches 0. Please

refer to Figure 28. Timing diagram in Auto-Reload mode (SWStart) and Figure 29. Timing diagram in Zero-Stop mode

(SWStart) for more details

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