ATmega8 Atmel Corporation, ATmega8 Datasheet - Page 203

• Manufacturer Part Number: ATmega8
• Manufacturer: Atmel Corporation

Specifications of ATmega8

• Flash (kbytes): 8 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 2
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 1
• 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: 3
• Output Compare Channels: 3
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

RWW – Read-While-
Write Section
NRWW – No Read-
While-Write Section
2486Z–AVR–02/11
If a Boot Loader software update is programming a page inside the RWW section, it is possible
to read code from the Flash, but only code that is located in the NRWW section. During an on-
going programming, the software must ensure that the RWW section never is being read. If the
user software is trying to read code that is located inside the RWW section (that is, by a
call/rjmp/lpm or an interrupt) during programming, the software might end up in an unknown
state. To avoid this, the interrupts should either be disabled or moved to the Boot Loader Sec-
tion. The Boot Loader Section is always located in the NRWW section. The RWW Section Busy
bit (RWWSB) in the Store Program memory Control Register (SPMCR) will be read as logical
one as long as the RWW section is blocked for reading. After a programming is completed, the
RWWSB must be cleared by software before reading code located in the RWW section.
“Store Program Memory Control Register – SPMCR” on page 206.
RWWSB.
The code located in the NRWW section can be read when the Boot Loader software is updating
a page in the RWW section. When the Boot Loader code updates the NRWW section, the CPU
is halted during the entire page erase or page write operation.
Table 77. Read-While-Write Features
Figure 101. Read-While-Write vs. No Read-While-Write
pointer Address during the
Which Section does the Z-
Programming?
NRWW section
RWW section
Z-pointer
Addresses RWW
section
Code Located in
NRWW Section
Can be Read during
the Operation
Which Section Can be
Programming?
NRWW section
Read during
Read-While-Write
No Read-While-Write
(RWW) Section
None
(NRWW) Section
Is the CPU
Halted?
Yes
No
Z-pointer
Addresses NRWW
section
CPU is Halted
during the Operation
for details on how to clear
ATmega8(L)
Read-While-
Supported?
Write
Yes
No
See
203