RM0312 datasheet(147/275 Pages) STMICROELECTRONICS

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RM0312

16-bit general purpose timer (TIM2/TIM3)

170

17.7.4

External trigger register (TIMx_ETR)

Address offset: 0x03

Reset value: 0x00

654

3210

ETP

ECE

ETPS[1:0]

ETF[3:0]

Bit 7 ETP: External trigger polarity

This bit selects whether ETR or ETR is used for trigger operations

0: ETR is non-inverted, active at high level or rising edge.

1: ETR is inverted, active at low level or falling edge.

Bit 6 ECE: External clock enable

This bit enables External clock mode 2.

0: External clock mode 2 disabled.

1: External clock mode 2 enabled. The counter is clocked by any active edge on the ETRF signal.

Note: Setting the ECE bit has the same effect as selecting the external clock mode 1 with TRGI

connected to ETRF (SMS=111 and TS=111 in the TIMx_SMCR register).

It is possible to use simultaneously the external clock mode 2 with the following modes: trigger

standard mode, trigger reset mode and trigger gated mode. Nevertheless, TRGI must not be

connected to ETRF in this case (TS bits must not be 111 in TIMx_SMCR register).

If external clock mode 1 and external clock mode 2 are enabled at the same time, the external

clock input will be ETRF.

Bits 5:4 ETPS: External trigger prescaler

External trigger signal ETRP frequency must be at must 1/4 of fMASTER frequency. A prescaler can

be enabled to reduce ETRP frequency. It is useful when inputting fast external clocks.

00: Prescaler OFF.

01: ETRP frequency divided by 2.

10: ETRP frequency divided by 4.

11: ETRP frequency divided by 8.

Bits 3:0 ETF: External trigger filter

This bit-field defines the frequency used to sample ETRP signal and the length of the digital filter

applied to ETRP. The digital filter is made of an event counter in which N events are needed to

validate a transition on the output:

0000: No filter, sampling is done at fMASTER

0001: fSAMPLING=fMASTER, N=2

0010: fSAMPLING=fMASTER, N=4

0011: fSAMPLING=fMASTER, N=8

0100: fSAMPLING=fMASTER/2, N=6

0101: fSAMPLING=fMASTER/2, N=8

0110: fSAMPLING=fMASTER/4, N=6

0111: fSAMPLING=fMASTER/4, N=8

1000: fSAMPLING=fMASTER/8, N=6

1001: fSAMPLING=fMASTER/8, N=8

1010: fSAMPLING=fMASTER/16, N=5

1011: fSAMPLING=fMASTER/16, N=6

1100: fSAMPLING=fMASTER/16, N=8

1101: fSAMPLING=fMASTER/32, N=5

1110: fSAMPLING=fMASTER/32, N=6

1111: fSAMPLING=fMASTER/32, N=8

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