AT90PWM1 Atmel Corporation, AT90PWM1 Datasheet - Page 76

• Manufacturer Part Number: AT90PWM1
• Manufacturer: Atmel Corporation

Specifications of AT90PWM1

• Flash (kbytes): 8 Kbytes
• Pin Count: 24
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 8
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 19
• Ext Interrupts: 4
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 125
• Analog Comparators: 2
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.5
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 105
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 12
• Input Capture Channels: 1
• Pwm Channels: 7
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

13. Timer/Counter0 and Timer/Counter1 Prescalers
13.0.1
13.0.2
13.0.3
76
AT90PWM1
Internal Clock Source
Prescaler Reset
External Clock Source
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
clock source. The prescaled clock has a frequency of either f
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 prescaler 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 prescaling 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 execu-
tion. 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 Tn/T0 pin can be used as Timer/Counter clock
(clk
logic. The synchronized (sampled) signal is then passed through the edge detector.
shows a functional equivalent block diagram of the Tn/T0 synchronization and edge detector
logic. The registers are clocked at the positive edge of the internal system clock (
is transparent in the high period of the internal system clock.
The edge detector generates one clk
(CSn2:0 = 6) edge it detects.
Figure 13-1. Tn/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 Tn/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn/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_I/O
T1
/clk
/1024.
Tn
clk
T0
I/O
). The Tn/T0 pin is sampled once every system clock cycle by the pin synchronization
CLK_I/O
D
LE
Q
). Alternatively, one of four taps from the prescaler can be used as a
Synchronization
D
Q
T1
/clk
T
0
pulse for each positive (CSn2:0 = 7) or negative
D
CLK_I/O
Q
/8, f
CLK_I/O
Edge Detector
/64, f
clk
CLK_I/O
4378C–AVR–09/08
I/O
Tn_sync
(To Clock
Select Logic)
Figure 13-1
). The latch
/256, or