em6521 EM Microelectronic, em6521 Datasheet - Page 35

• Manufacturer Part Number: em6521
• Description: Mfp Version Of Em6621 Ultra Low Power Microcontroller With 4x20 Lcd Driver
• Manufacturer: EM Microelectronic

Figure 25. PWM Output in Up Count Mode
For instance, loading the counter in up count mode with hex 000 and the comparator with hex C52 which will
be identified as :
Thus after 5 PWM-pulses of 2 clocks cycles length the Counter generates an IRQComp and stops.
The same example with SelIntFull=0 (limited bit compare) will produce an unlimited number of PWM at a length
of 2 clock cycles.
8.5.1 How the PWM Generator works.
For Up Count Mode ; Setting the counter in up count and PWM mode the PB[3] PWM output is defined to be 0
( EnComp =0 forces the PWM output to 0 in upcount mode, 1 in downcount). Each Roll Over will set the output
to ‘1’ and each Compare Match will set it back to ‘0’. The Compare Match for PWM always only works on the
defined counter length. This, independent of the SelIntFull setting which is valid only for the IRQ generation.
Refer also to the compare setup in chapter
In above example the PWM starts counting up on hex 0,
The normal IRQ generation remains on during PWM output. If no IRQ’s are wanted, the corresponding masks
need to be set.
In Down Count Mode everything is inverted. The PWM output starts with the ‘1’ value. Each Roll Over will set
the output to ‘0’ and each Compare Match will set it back to ‘1’. For limited pulse generation one must load the
complementary pulse number value. I.e. for 5 pulses counting on 4 bits load bits[9 :4] with hex 3A (bin
111010).
8.5.2 PWM Characteristics
PWM resolution is
the minimal signal period is
the maximum signal period is
the minimal pulse width is
* This values are for Fmax or Fmin derived from the internal system clock (32kHz). Much shorter (and longer)
PWM pulses can be achieved by using the port A as frequency input.
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 downcount mode.
Copyright © 2005, EM Microelectronic-Marin SA
PWM output
Count[9 :0]
Roll-over
Compare
IRQCount0
IRQComp
Clock
03E
- bits[11:10] are limiting the counter to limits to 4 bits length, =03
- bits
- bits
2 cycles later compare match -> PWM to ‘0’,
14 cycles later roll over -> PWM to ‘1’
2 cycles later compare match -> PWM to ‘0’ , etc. until the completion of the 5 pulses.
03F
R
[9:4] are the unused counter bits = hex 05 (bin 000101),
[3:0] (comparator value = 2).
000
001
...
: 10bits (1024 steps), 8bits (256 steps), 6bits (64 steps) or 4 bits (16 steps)
: 16 (4-bit) x Fmax*
: 1024 x Fmin*
: 1 bit
Data-1
Data
Data+1
8 .4.
1 3 3 H
Data+2
-> 16 x 1/Ck[15]
-> 1024 x 1/Ck[1]
-> 1 x 1/Ck[15]
Figure 26. PWM Output in Down Count Mode
Roll-over
IRQCount0
IRQComp
PWM output
Count[9 :0]
Compare
Clock
35
001
000
3FF
3FE
(BitSel[1,0])
(number of PWM pulses)
(length of PWM pulse)
-> 977 µs
-> 1024 s
-> 61 µs
...
Data+1
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EM6521
Data
(32 KHz)
(32 KHz)
(32 KHz)
Data-1
Data-2