ATtiny5 Atmel Corporation, ATtiny5 Datasheet - Page 61

• Manufacturer Part Number: ATtiny5
• Manufacturer: Atmel Corporation

Specifications of ATtiny5

• Flash (kbytes): 0.5 Kbytes
• Pin Count: 6
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 1
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 4
• Ext Interrupts: 4
• Usb Speed: No
• Usb Interface: No
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 4
• Adc Resolution (bits): 8
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.03
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 125
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 1
• Output Compare Channels: 2
• Input Capture Channels: 1
• Pwm Channels: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

11.6.1
11.6.2
11.6.3
8127E–AVR–11/11
Force Output Compare
Compare Match Blocking by TCNT0 Write
Using the Output Compare Unit
double buffering is disabled. The double buffering synchronizes the update of the OCR0x Com-
pare Register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the out-
put glitch-free.
The OCR0x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR0x Buffer Register, and if double buffering is dis-
abled the CPU will access the OCR0x directly. The content of the OCR0x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT0 and ICR0 Register). Therefore OCR0x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as when
accessing other 16-bit registers. Writing the OCR0x Registers must be done via the TEMP Reg-
ister since the compare of all 16 bits is done continuously. The high byte (OCR0xH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
updated by the value written. Then when the low byte (OCR0xL) is written to the lower eight bits,
the high byte will be copied into the upper 8-bits of either the OCR0x buffer or OCR0x Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to
on page
In non-PWM Waveform Generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (0x) bit. Forcing compare match will not set the
OCF0x flag or reload/clear the timer, but the OC0x pin will be updated as if a real compare
match had occurred (the COM01:0 bits settings define whether the OC0x pin is set, cleared or
toggled).
All CPU writes to the TCNT0 Register will block any compare match that occurs in the next timer
clock cycle, even when the timer is stopped. This feature allows OCR0x to be initialized to the
same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is enabled.
Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT0 when using any of the Output Compare
channels, independent of whether the Timer/Counter is running or not. If the value written to
TCNT0 equals the OCR0x value, the compare match will be missed, resulting in incorrect wave-
form generation. Do not write the TCNT0 equal to TOP in PWM modes with variable TOP
values. The compare match for the TOP will be ignored and the counter will continue to 0xFFFF.
Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is downcounting.
The setup of the OC0x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0x value is to use the Force Output Com-
pare (0x) strobe bits in Normal mode. The OC0x Register keeps its value even when changing
between Waveform Generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value.
Changing the COM0x1:0 bits will take effect immediately.
72.
“Accessing 16-bit Registers”
ATtiny4/5/9/10
61