ATA6602-EK Atmel, ATA6602-EK Datasheet - Page 112

• Manufacturer Part Number: ATA6602-EK
• Manufacturer: Atmel

Specifications of ATA6602-EK

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4.12.1.1
4.12.1.2
4.12.2
112
ATA6602/ATA6603
Timer/Counter Clock Sources
Definitions
Registers
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-
pare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in
Table 4-43.
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the
Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Inter-
rupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clk
The double buffered Output Compare Registers (OCR0A and OCR0B) are compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Gen-
erator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and
OC0B). See
event will also set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Out-
put Compare interrupt request.
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and pres-
caler (see
BOTTOM
MAX
TOP
“Timer/Counter0 and Timer/Counter1 Prescalers” on page
“Using the Output Compare Unit” on page 141
General Counter Definitions
The counter reaches the BOTTOM when it becomes 0x00.
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be the fixed value 0xFF
(MAX) or the value stored in the OCR0A Register. The assignment is dependent
on the mode of operation.
Table 4-43
are also used extensively throughout the document.
for details. The compare match
129).
4921E–AUTO–09/09
T0
).