EM6821 datasheet(33/68 Pages) EMMICRO

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EM6821

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8.3 Event Counting

The counter can be used in a special event count mode where a certain number of events (clocks) on the PA[0]

or PA[3] input are counted. In this mode the counting will start directly on the next active clock edge on the

selected port A input.

The Event Count mode is switched on by setting bit EvCount in the register RegCCntl2 to ‘1’.PA[3] and PA[0]

inputs can be inverted depending on register OPTIntEdgPA and should be debounced. The debouncer is

switched on in register OPTDebIntPA bits NoDebIntPA[3,0]=0. Its frequency depends on the bit DebSel from

IntEdgPA[3] respectively IntEdgPA[0] equal

1. Refer also

to Figure 10 for internal clock signal

generation.

8.4 Compare Function

A previously loaded register value (CReg[9:0]) can be compared against the actual counter value

(Count[9:0]). If the two are matching (equality) then an interrupt (IRQComp) is generated. The compare

function is switched on with the bit EnComp in the register RegCCntl2. With EnComp = 0 no IRQComp is

generated. Starting the counter with the same value as the compare register is possible, no IRQ is generated

on start. Full or Limited bit compare are possible, defined by bit SelIntFull in register RegSysCntl1.

EnComp must be written after a load operation (Load = 1). Every load operation resets the bit EnComp.

Full bit compare function.

Bit SelIntFull is set to ‘1’. The function behaves as described above independent of the selected counter

length. Limited bit counting together with full bit compare can be used to generate a certain amount of

IRQCount0 interrupts until the counter generates the IRQComp interrupt. With PWMOn=‘1’ the counter would

have automatically stopped after the IRQComp, with PWMOn=‘0’ it will continue until the software stops it.

EnComp must be cleared before setting SelIntFull and before starting the counter again. Be careful, PWMOn

also redefines the port B PB[3] output data.(refer to section 8.5).

Limited bit compare

With the bit SelIntFull set to ‘0’ (default) the compare function will only take as many bits into account as

defined by the counter length selection BitSel[1:0] (see chapter 8.1).

8.5 Pulse Width Modulation (PWM)

The PWM generator uses the behavior of the Compare function (see above) so EnComp must be set to

activate the PWM function.. At each Roll Over or Compare Match the PWM state - which is output on port B

PB[3] - will toggle. The start value on PB[3] is forced while EnComp is 0 the value is depending on the up or

down count mode. Every counter value load operation resets the bit EnComp and therefore the PWM start

value is reinstalled.

Setting PWMOn to ‘1’ in register RegPresc routes the counter PWM output to port B terminal PB[3]. Insure that

PB[3] is set to output mode . Refer to section 6.4 for the port B setup.

The PWM signal generation is independent of the limited or full bit compare selection bit SelIntFull. However if

SelIntFull = 1 (FULL) and the counter compare function is limited to lower than 10 bits one can generate a

predefined number of output pulses. In this case, the number of output pulses is defined by the value of the

unused counter bits. It will count from the start value until the IRQComp match.

One must not use a compare value of hex 0 in up count mode nor a value of hex 3FF (or FF,3F, F if limited bit

compare) in down count mode.

Figure 24. Internal Clock Synchronization

Start

Count[9:0

]

+ / - 1

EvCount = 0

Start

EvCount = 0

Start

EvCount = 1

Start

EvCount = 1

Count[9:0

]

+ / - 1

Count[9:0

]

Count[9:0

]

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