ATMEGA8535L-8AC Atmel, ATMEGA8535L-8AC Datasheet - Page 87

• Manufacturer Part Number: ATMEGA8535L-8AC
• Description: IC AVR MCU 8K LV 8MHZ COM 44TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8535L-8AC

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Timer/Counter0 and
Timer/Counter1
Prescalers
Internal Clock Source
Prescaler Reset
External Clock Source
2502K–AVR–10/06
Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the
Timer/Counters can have different prescaler settings. The description below applies to
both Timer/Counter1 and Timer/Counter0.
The Timer/Counter can be clocked directly by the system clock (by setting the
CSn2:0 = 1). This provides the fastest operation, with a maximum Timer/Counter clock
frequency equal to system clock frequency (f
the prescaler can be used as a clock source. The prescaled clock has a frequency of
either f
The prescaler is free running (i.e., operates independently of the clock select logic of the
Timer/Counter) and it is shared by Timer/Counter1 and Timer/Counter0. Since the pres-
caler is not affected by the Timer/Counter’s clock select, the state of the prescaler will
have implications for situations where a prescaled clock is used. One example of pres-
caling artifacts occurs when the timer is enabled and clocked by the prescaler
(6 > CSn2:0 > 1). The number of system clock cycles from when the timer is enabled to
the first count occurs can be from 1 to N+1 system clock cycles, where N equals the
prescaler divisor (8, 64, 256, or 1024).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program
execution. However, care must be taken if the other Timer/Counter that shares the
same prescaler also uses prescaling. A prescaler reset will affect the prescaler period
for all Timer/Counters it is connected to.
An external clock source applied to the T1/T0 pin can be used as Timer/Counter clock
(clk
chronization logic. The synchronized (sampled) signal is then passed through the edge
detector. Figure 38 shows a functional equivalent block diagram of the T1/T0 synchroni-
zation and edge detector logic. The registers are clocked at the positive edge of the
internal system clock (
system clock.
The edge detector generates one clk
ative (CSn2:0 = 6) edge it detects.
Figure 38. T1/T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system
clock cycles from an edge has been applied to the T1/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when T1/T0 has been stable for
at least one system clock cycle, otherwise it is a risk that a false Timer/Counter clock
pulse is generated.
clk
Tn
T1
I/O
/clk
CLK_I/O
T0
). The T1/T0 pin is sampled once every system clock cycle by the pin syn-
D
LE
/8, f
Q
CLK_I/O
Synchronization
D
/64, f
clk
I/O
Q
). The latch is transparent in the high period of the internal
CLK_I/O
/256, or f
T1
/clk
T
0
CLK_I/O
pulse for each positive (CSn2:0 = 7) or neg-
CLK_I/O
/1024.
). Alternatively, one of four taps from
D
Q
ATmega8535(L)
Edge Detector
Tn_sync
(To Clock
Select Logic)
87