ST10F280 datasheet(65/186 Pages) STMICROELECTRONICS

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ST10F280

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11.2.1.4 - Single Shot Mode

Single shot mode is selected by setting the

respective bit PSx in register XPWMCON1 to ‘1’.

This mode is available for XPWM channels 2

and 3.

In this mode the timer XPTx of the respective

XPWM channel is started via software and is

counting up until it reaches the value in the asso-

ciated period shadow register. Upon the next

count pulse the timer is cleared to 0000h and

stopped via hardware, i.e. the respective PTRx bit

is cleared. The XPWM output signal is switched to

high level when the timer contents are equal to or

greater than the contents of the pulse width

shadow register. The signal is switched back to

low level when the respective timer is cleared, i.e.

is below the pulse width shadow register. Thus

starting a XPWM timer in single shot mode pro-

duces one single pulse on the respective port pin,

provided that the pulse width value is between

0000h and the period value. In order to generate a

further pulse, the timer has to be started again via

software by setting bit PTRx (see Figure 23).

After starting the timer (i.e. PTRx = ‘1’) the output

pulse may be modified via software. Writing to

timer XPTx changes the positive and/or negative

edge of the output signal, depending on whether

the pulse has already started (i.e. the output is

high) or not (i.e. the output is still low). This (multi-

ple) re-triggering is always possible while the

timer is running, i.e. after the pulse has started

and before the timer is stopped.

Loading counter XPTx directly with the value in

the respective XPPx shadow register will abort the

current PWM pulse upon the next clock pulse

(counter is cleared and stopped by hardware).

By setting the period (XPPx), the timer start value

(XPTx) and the pulse width value (XPWx) appro-

priately, the pulse width (tw) and the optional

pulse delay (td) may be varied in a wide range.

Figure 23 : Operation and Output Waveform in Single Shot Mode

XPPx

Period=7

XPTx Count

Value

XPWx Pulse

Width=4

Set PTRx

by Software

PTRx Reset

by Hardware

PTx stopped

Set PTRx

by Software

LSR

for Next Pulse

XPPx

Period=7

XPTx Count

Value

XPWx Pulse

Width=4

Retrigger after

Write PWx value to PTx

Trigger before Pulse has started :

Write PWx value to PTx;

LSR

Shortens Delay Time tD

Pulse has started :

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