ATMEGA8535-16PU Atmel, ATMEGA8535-16PU Datasheet - Page 91

• Manufacturer Part Number: ATMEGA8535-16PU
• Description: IC AVR MCU 8K 16MHZ 5V 40DIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8535-16PU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• 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): 4.5 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Processor Series: ATMEGA8x
• Core: AVR8
• Data Bus Width: 8 bit
• Data Ram Size: 512 B
• Interface Type: 2-Wire, SPI, USART
• Maximum Clock Frequency: 16 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 4.5 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• 3rd Party Development Tools: EWAVR, EWAVR-BL
• Development Tools By Supplier: ATAVRDRAGON, ATSTK500, ATSTK600, ATAVRISP2, ATAVRONEKIT
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit, 8 Channel
• A/d Inputs: 8-Channel, 10-Bit
• Cpu Speed: 16 MIPS
• Eeprom Memory: 512 Bytes
• Input Output: 32
• Interface: SPI/TWI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 40-pin PDIP
• Programmable Memory: 8K Bytes
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 4.5-5.5 V
• Controller Family/series: AVR MEGA
• No. Of I/o's: 32
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 512Byte
• Rohs Compliant: Yes
• For Use With: ATSTK600 - DEV KIT FOR AVR/AVR32770-1007 - ISP 4PORT ATMEL AVR MCU SPI/JTAGATAVRISP2 - PROGRAMMER AVR IN SYSTEMATSTK500 - PROGRAMMER AVR STARTER KIT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Accessing 16-bit
Registers
2502G–AVR–04/05
The TCNT1, OCR1A/B, and ICR1 are 16-bit registers that can be accessed by the AVR
CPU via the 8-bit data bus. The 16-bit register must be byte accessed using two read or
write operations. Each 16-bit timer has a single 8-bit register for temporary storing of the
high byte of the 16-bit access. The same temporary register is shared between all 16-bit
registers within each 16-bit timer. Accessing the low byte triggers the 16-bit read or write
operation. When the low byte of a 16-bit register is written by the CPU, the high byte
stored in the temporary register, and the low byte written are both copied into the 16-bit
register in the same clock cycle. When the low byte of a 16-bit register is read by the
CPU, the high byte of the 16-bit register is copied into the temporary register in the
same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the
OCR1A/B 16-bit registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read,
the low byte must be read before the high byte.
The following code examples show how to access the 16-bit Timer Registers assuming
that no interrupts update the temporary register. The same principle can be used directly
for accessing the OCR1A/B and ICR1 Registers. Note that when using “C”, the compiler
handles the 16-bit access.
Note:
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an inter-
rupt occurs between the two instructions accessing the 16-bit register, and the interrupt
code updates the temporary register by accessing the same or any other of the 16-bit
Timer Registers, then the result of the access outside the interrupt will be corrupted.
Therefore, when both the main code and the interrupt code update the temporary regis-
ter, the main code must disable the interrupts during the 16-bit access.
Assembly Code Examples
C Code Examples
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in
in
...
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...
1. See “About Code Examples” on page 6.
r16,TCNT1L
r17,TCNT1H
(1)
(1)
ATmega8535(L)
91