ATmega8515 Atmel Corporation, ATmega8515 Datasheet - Page 107
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ATmega8515
Manufacturer Part Number
ATmega8515
Description
Manufacturer
Atmel Corporation
Specifications of ATmega8515
Flash (kbytes)
8 Kbytes
Pin Count
44
Max. Operating Frequency
16 MHz
Cpu
8-bit AVR
# Of Touch Channels
16
Hardware Qtouch Acquisition
No
Max I/o Pins
35
Ext Interrupts
3
Usb Speed
No
Usb Interface
No
Spi
1
Uart
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
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 85
I/o Supply Class
2.7 to 5.5
Operating Voltage (vcc)
2.7 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
2
Output Compare Channels
3
Input Capture Channels
1
Pwm Channels
3
32khz Rtc
No
Calibrated Rc Oscillator
Yes
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Force Output Compare
Compare Match Blocking by
TCNT1 Write
Using the Output Compare
Unit
2512K–AVR–01/10
sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical
PWM pulses, thereby making the output glitch-free.
The OCR1x Register access may seem complex, but this is not case. When the double
buffering is enabled, the CPU has access to the OCR1x Buffer Register, and if double
buffering is disabled the CPU will access the OCR1x directly. The content of the OCR1x
(Buffer or Compare) Register is only changed by a write operation (the Timer/Counter
does not update this register automatically as the TCNT1 – and ICR1 Register). There-
fore OCR1x 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 OCR1x Registers must be done via the TEMP Register since the compare of all 16
bits is done continuously. The high byte (OCR1xH) 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 (OCR1xL) is written to the lower eight bits, the high byte
will be copied into the upper eight bits of either the OCR1x Buffer or OCR1x Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit
Registers” on page 100.
In non-PWM Waveform Generation modes, the match output of the comparator can be
forced by writing a one to the Force Output Compare (FOC1x) bit. Forcing Compare
Match will not set the OCF1x Flag or reload/clear the timer, but the OC1x pin will be
updated as if a real Compare Match had occurred (the COM11:0 bits settings define
whether the OC1x pin is set, cleared or toggled).
All CPU writes to the TCNT1 Register will block any Compare Match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR1x to be
initialized to the same value as TCNT1 without triggering an interrupt when the
Timer/Counter clock is enabled.
Since writing TCNT1 in any mode of operation will block all Compare Matches for one
timer clock cycle, there are risks involved when changing TCNT1 when using any of the
output compare channels, independent of whether the Timer/Counter is running or not.
If the value written to TCNT1 equals the OCR1x value, the Compare Match will be
missed, resulting in incorrect waveform generation. Do not write the TCNT1 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 TCNT1 value
equal to BOTTOM when the counter is downcounting.
The setup of the OC1x should be performed before setting the Data Direction Register
for the port pin to output. The easiest way of setting the OC1x value is to use the Force
Output Compare (FOC1x) strobe bits in Normal mode. The OC1x Register keeps its
value even when changing between Waveform Generation modes.
Be aware that the COM1x1:0 bits are not double buffered together with the compare
value. Changing the COM1x1:0 bits will take effect immediately.
ATmega8515(L)
107