ATA5771-DK1 Atmel, ATA5771-DK1 Datasheet - Page 82

• Manufacturer Part Number: ATA5771-DK1
• Description: BOARD XMITTER FOR ATA5771 868MHZ
• Manufacturer: Atmel
• Type: Transmitterr

Specifications of ATA5771-DK1

• Frequency: 868MHz
• Maximum Frequency: 868 MHz
• Supply Voltage (max): 4 V
• Supply Voltage (min): 2 V
• Supply Current: 8.5 mA
• Product: RF Development Tools
• For Use With/related Products: ATA5771
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

4.15.7.1
4.15.7.2
82
Atmel ATA5771/73/74
Normal Mode
Clear Timer on Compare Match (CTC) Mode
For detailed timing information refer to
ure 4-35 on page 87
Diagrams” on page
The simplest mode of operation is the Normal mode (WGM02:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bot-
tom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the
same timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like
a ninth bit, except that it is only set, not cleared. However, combined with the timer overflow
interrupt that automatically clears the TOV0 Flag, the timer resolution can be increased by
software. There are no special cases to consider in the Normal mode, a new counter value
can be written anytime.
The Output Compare Unit can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
In Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used to
manipulate the counter resolution. In CTC mode the counter is cleared to zero when the coun-
ter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter,
hence also its resolution. This mode allows greater control of the Compare Match output fre-
quency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 4-30. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using
the OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for
updating the TOP value. However, changing TOP to a value close to BOTTOM when the
counter is running with none or a low prescaler value must be done with care since the CTC
mode does not have the double buffering feature. If the new value written to OCR0A is lower
than the current value of TCNT0, the counter will miss the Compare Match. The counter will
then have to count to its maximum value (0xFF) and wrap around starting at 0x00 before the
Compare Match can occur.
TCNTn
OCn
(Toggle)
Period
86.
1
and
Figure 4-36 on page 87
2
Figure 4-33 on page
3
in
Figure
4
Section 4.15.8 “Timer/Counter Timing
4-30. The counter value (TCNT0)
86,
Figure 4-34 on page
OCnx Interrupt Flag Set
(COMnx1:0 = 1)
9137E–RKE–12/10
87,
Fig-