BLUENRG-2 datasheet(130/190 Pages) STMICROELECTRONICS

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Functional details

BlueNRG-2

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DocID030675 Rev 2

This mode is a combination of mode 3 and mode 2,and makes it possible to operate

Timer/Counter 2 as a single input-capture timer while Timer/Counter 1 can be used as a

system timer as described above.

TnCNT1 starts counting down once a clock has been enabled. Upon underflow, TnCNT1 is

reloaded from the TnCRB register, and counting proceeds downward from that value. If

enabled, the TnA pin toggles upon every underflow of TnCNT1. The initial value of the TnA

output signal can be selected by software to be either high or low. In addition, the TnAPND

interrupt-pending flag is set and a timer interrupt 1 is generated if the TnAIEN bit is set.

Since TnA toggles upon every underflow, a 50% duty-cycle PWM signal can be generated

on TnA without requiring any interaction with the software or the CPU.

TnCNT2 starts counting down once a clock has been enabled. When a transition is

received on TnB, the value contained in TnCNT2 is transferred to TnCRB, and the

interrupt-pending flag TnBPND is set. A timer interrupt 1is generated if enabled. The

software can enable a pReset of the counter to 0xFFFF upon detection of a transition on

TnB. In this case, the current value of TnCNT2 is transferred to TnCRB, followed by a

pReset of the counter to 0xFFFF. TnCNT2 starts counting downwards from 0xFFFF until

the next transition is received on TnB, which causes the procedure of capture and pReset

to be repeated. The underflow of TnCNT2 causes the TnDPND interrupt-pending flag to be

set, and can also generate a timer interrupt 2 if enabled. The input signal on TnB must

have a pulse width equal to or greater than one system clock cycle. TnB can be configured

to sense either rising or falling edges. TnCNT2 cannot operate in the pulse-accumulate or

external-event counter modes since the TnB input is used as a capture input. Selecting

either of these modes for TnCNT2 causes TnCNT2 to be stopped. However, all available

clock source modes may be selected for TnCNT1. Thus by using TnCNT1, it is possible to

determine the number of capture events on TnB, or the elapsed time between capture

events on TnB.

3.13.2.6

Timer IO functions

There are two pins associated with each instance of the MFTX. The pins are called TnA

and TnB. The functionality of TnA and TnB depends on the mode of operation and the

value of the TnAEN and TnBEN bits. Table 157: "MFT IO functions" shows the function of

TnA and TnB for various modes of operation. Note that if TnA functions as a PWM output,

TnAOUT defines the initial and present value of TnA. For example, if the user wishes to

start with TnA high, TnAOUT needs to be set before enabling the timer clock.

Table 157: MFT IO functions

TnAEN

TnBEN

Mode 1

Mode 1a

Mode 2

Mode 3

Mode 4

PWM and

counter

PWM pulse

train

Dual-input

capture and

counter

Dual

independent

counter

Input capture

plus timer

TnA

TnAEN

= 0

TnBEN

= X

No output

Capture

TnCNT1 into

TnCRB

No output toggle

No output

toggle

TnAEN

= 1

TnBEN

= X

Toggle output

on underflow

of TnCNT1

Toggle

output on

underflow of

TnCNT1

Capture

TnCNT1 into

TnCRA and

preset

TnCNT1

Toggle output

on underflow

of TnCNT1

TnB

TnAEN

= X

TnBEN

= 0

External event

or pulse

accumulate

input

External

event if

TnPTSE = 0

Capture

TnCNT1 into

TnCRB

External event

or pulse

accumulate

input

Capture

TnCNT2 into

TnCRB

BLUENRG-2 Datasheet(PDF) 130 Page - STMicroelectronics

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