EM6821 datasheet(35/68 Pages) EMMICRO

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EM6821

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8.6 Counter Setup

RegCDataL[3:0],

RegCDataM[3:0], RegCDataH[1:0] are used to store the initial count value called

CReg[9:0] which is written into the count register bits Count[9:0] when writing the bit Load to ‘1’ in

RegCCntl2. This bit is automatically reset thereafter. The counter value Count[9:0] can be read out at any

time, except when using non-debounced high frequency port A input clock. To maintain data integrity the lower

nibble Count[3:0] must always be read first. The ShCount[9:4] values are shadow registers to the counter. To

keep the data integrity during a counter read operation (3 reads), the counter values [9:4] are copied into these

registers with the read of the count[3:0] register. If using non-debounced high frequency port A input the

counter must be stopped while reading the Count[3:0] value to maintain the data integrity.

In down count mode an interrupt request IRQCount0 is generated when the counter reaches 0. In up count

mode, an interrupt request is generated when the counter reaches 3FF (or FF,3F,F if limited bit counting).

Never an interrupt request is generated by loading a value into the counter register.

When the counter is programmed from up into down mode or vice versa, the counter value Count[9:0] gets

inverted. As a consequence, the initial value of the counter must be programmed after the Up/Down selection.

Loading the counter with hex 000 is equivalent to writing stop mode, the Start bit is reset, no interrupt request

is generated.

How to use the counter;

If PWM output is required one has to put the port B[3] in output mode and set PWMOn=1 in step 5.

1st,

set the counter into stop mode (Start=0).

2nd,

select the frequency and up- or down count mode in RegCCntl1.

3rd,

write the data registers RegCDataL, RegCDataM, RegCDataH (counter start value and

length)

4th,

load the counter, Load=1, and choose the mode. (EvCount, EnComp=0)

5th,

select bits PWMOn in RegPresc and SelIntFull in RegSysCntl1

6th,

if compare mode desired , then write RegCDataL, RegCDataM, RegCDataH (compare value)

7th,

set bit Start and select EnComp in RegCCntl2

8.7 10-bit Counter Registers

Table 8.7.1 Register RegCCntl1

Bit

Name

Reset

R/W

Description

Up/Down

R/W

Up or down counting

CountFSel2

R/W

Input clock selection

CountFSel1

R/W

Input clock selection

CountFsel0

R/W

Input clock selection

Default : PA0 ,selected as input clock, Down counting

Table 8.7.2 Counter Input Frequency Selection with CountFSel[2..0]

CountFSel2

CountFSel1

CountFSel0

clock source selection

Port A

PA[0]

Prescaler Ck[15]

Prescaler Ck[12]

Prescaler Ck[10]

Prescaler Ck[8]

Prescaler Ck[4]

Prescaler Ck[1]

Port A

PA[3]

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