- •Features
- •Pin Configurations
- •Overview
- •Block Diagram
- •Pin Descriptions
- •Port A (PA7..PA0)
- •Port B (PB7..PB0)
- •Port C (PC7..PC0)
- •Port D (PD7..PD0)
- •Port E (PE7..PE0)
- •Port F (PF7..PF0)
- •Port G (PG4..PG0)
- •RESET
- •XTAL1
- •XTAL2
- •AVCC
- •AREF
- •AVR CPU Core
- •Introduction
- •Architectural Overview
- •Status Register
- •Stack Pointer
- •Interrupt Response Time
- •SRAM Data Memory
- •Data Memory Access Times
- •EEPROM Data Memory
- •EEPROM Read/Write Access
- •I/O Memory
- •Overview
- •ATmega103 Compatibility
- •Address Latch Requirements
- •Pull-up and Bus-keeper
- •Timing
- •XMEM Register Description
- •Using all 64KB Locations of External Memory
- •Clock Systems and their Distribution
- •CPU Clock – clkCPU
- •I/O Clock – clkI/O
- •Flash Clock – clkFLASH
- •ADC Clock – clkADC
- •Clock Sources
- •Crystal Oscillator
- •External RC Oscillator
- •External Clock
- •Timer/Counter Oscillator
- •Idle Mode
- •Power-down Mode
- •Power-save Mode
- •Standby Mode
- •Extended Standby Mode
- •Analog to Digital Converter
- •Analog Comparator
- •Brown-out Detector
- •Internal Voltage Reference
- •Watchdog Timer
- •Port Pins
- •System Control and Reset
- •Resetting the AVR
- •Reset Sources
- •Power-on Reset
- •External Reset
- •Brown-out Detection
- •Watchdog Reset
- •Watchdog Timer
- •Timed Sequences for Changing the Configuration of the Watch Dog Timer
- •Safety Level 0
- •Safety Level 1
- •Safety Level 2
- •Interrupts
- •I/O-Ports
- •Introduction
- •Configuring the Pin
- •Reading the Pin Value
- •Alternate Port Functions
- •Alternate Functions of Port A
- •Alternate Functions of Port B
- •Alternate Functions of Port C
- •Alternate Functions of Port D
- •Alternate Functions of Port E
- •Alternate Functions of Port F
- •Alternate Functions of Port G
- •Port A Data Register – PORTA
- •Port B Data Register – PORTB
- •Port C Data Register – PORTC
- •Port D Data Register – PORTD
- •Port E Data Register – PORTE
- •Port F Data Register – PORTF
- •Port G Data Register – PORTG
- •External Interrupts
- •8-bit Timer/Counter0 with PWM and Asynchronous Operation
- •Overview
- •Registers
- •Definitions
- •Counter Unit
- •Output Compare Unit
- •Force Output Compare
- •Modes of Operation
- •Normal Mode
- •Fast PWM Mode
- •Phase Correct PWM Mode
- •Timer/Counter Prescaler
- •16-bit Timer/Counter (Timer/Counter1 and Timer/Counter3)
- •Overview
- •Registers
- •Definitions
- •Compatibility
- •Counter Unit
- •Input Capture Unit
- •Input Capture Trigger Source
- •Noise Canceler
- •Using the Input Capture Unit
- •Output Compare Units
- •Force Output Compare
- •Modes of Operation
- •Normal Mode
- •Fast PWM Mode
- •Phase Correct PWM Mode
- •16-bit Timer/Counter Register Description
- •Internal Clock Source
- •Prescaler Reset
- •External Clock Source
- •8-bit Timer/Counter2 with PWM
- •Overview
- •Registers
- •Definitions
- •Counter Unit
- •Output Compare Unit
- •Force Output Compare
- •Modes of Operation
- •Normal Mode
- •Fast PWM Mode
- •Phase Correct PWM Mode
- •Overview
- •Description
- •Timing Example
- •Slave Mode
- •Master Mode
- •SPI Control Register – SPCR
- •SPI Status Register – SPSR
- •SPI Data Register – SPDR
- •Data Modes
- •USART
- •Dual USART
- •Overview
- •AVR USART vs. AVR UART – Compatibility
- •Clock Generation
- •External Clock
- •Synchronous Clock Operation
- •Frame Formats
- •Parity Bit Calculation
- •USART Initialization
- •Sending Frames with 5 to 8 Data Bit
- •Sending Frames with 9 Data Bit
- •Parity Generator
- •Disabling the Transmitter
- •Receiving Frames with 5 to 8 Data Bits
- •Receiving Frames with 9 Data Bits
- •Receiver Error Flags
- •Parity Checker
- •Disabling the Receiver
- •Flushing the Receive Buffer
- •Asynchronous Data Recovery
- •Using MPCM
- •Two-wire Serial Interface
- •Features
- •TWI Terminology
- •Electrical Interconnection
- •Transferring Bits
- •START and STOP Conditions
- •Address Packet Format
- •Data Packet Format
- •Multi-master Bus Systems, Arbitration and Synchronization
- •Overview of the TWI Module
- •Scl and SDA Pins
- •Bit Rate Generator Unit
- •Bus Interface Unit
- •Address Match Unit
- •Control Unit
- •TWI Register Description
- •TWI Bit Rate Register – TWBR
- •TWI Control Register – TWCR
- •TWI Status Register – TWSR
- •TWI Data Register – TWDR
- •Using the TWI
- •Transmission Modes
- •Master Transmitter Mode
- •Master Receiver Mode
- •Slave Receiver Mode
- •Slave Transmitter Mode
- •Miscellaneous States
- •Analog Comparator
- •Analog Comparator Multiplexed Input
- •Analog to Digital Converter
- •Features
- •Operation
- •Starting a Conversion
- •Differential Gain Channels
- •ADC Input Channels
- •ADC Voltage Reference
- •ADC Noise Canceler
- •Analog Input Circuitry
- •ADC Accuracy Definitions
- •ADC Conversion Result
- •ADLAR = 0:
- •ADLAR = 1:
- •Features
- •Overview
- •Test Access Port – TAP
- •TAP Controller
- •PRIVATE0; $8
- •PRIVATE1; $9
- •PRIVATE2; $A
- •PRIVATE3; $B
- •Bibliography
- •Features
- •System Overview
- •Data Registers
- •Bypass Register
- •Device Identification Register
- •Reset Register
- •Boundary-scan Chain
- •EXTEST; $0
- •IDCODE; $1
- •SAMPLE_PRELOAD; $2
- •AVR_RESET; $C
- •BYPASS; $F
- •Boundary-scan Chain
- •Scanning the Digital Port Pins
- •Scanning the RESET Pin
- •Scanning the Clock Pins
- •Scanning the ADC
- •Boot Loader Features
- •Application Section
- •Boot Loader Section – BLS
- •Boot Loader Lock Bits
- •Performing a Page Write
- •Using the SPM Interrupt
- •Setting the Boot Loader Lock Bits by SPM
- •Reading the Fuse and Lock Bits from Software
- •Preventing Flash Corruption
- •Simple Assembly Code Example for a Boot Loader
- •Fuse Bits
- •Latching of Fuses
- •Signature Bytes
- •Calibration Byte
- •Signal Names
- •Parallel Programming
- •Enter Programming Mode
- •Chip Erase
- •Programming the Flash
- •Programming the EEPROM
- •Reading the Flash
- •Reading the EEPROM
- •Programming the Lock Bits
- •Reading the Signature Bytes
- •Reading the Calibration Byte
- •Serial Downloading
- •Data Polling Flash
- •Data Polling EEPROM
- •AVR_RESET ($C)
- •PROG_ENABLE ($4)
- •PROG_COMMANDS ($5)
- •PROG_PAGELOAD ($6)
- •PROG_PAGEREAD ($7)
- •Data Registers
- •Reset Register
- •Programming Enable Register
- •Virtual Flash Page Read Register
- •Programming Algorithm
- •Entering Programming Mode
- •Leaving Programming Mode
- •Performing Chip Erase
- •Programming the Flash
- •Reading the Flash
- •Programming the EEPROM
- •Reading the EEPROM
- •Programming the Fuses
- •Programming the Lock Bits
- •Reading the Signature Bytes
- •Reading the Calibration Byte
- •Electrical Characteristics
- •Absolute Maximum Ratings*
- •DC Characteristics
- •External Clock Drive Waveforms
- •External Clock Drive
- •2-wire Serial Interface Characteristics
- •ADC Characteristics - Preliminary Data
- •External Data Memory Timing
- •Ordering Information
- •Packaging Information
Voltage Reference Enable The voltage reference has a start-up time that may influence the way it should be used. Signals and Start-up Time The start-up time is given in Table 20. To save power, the reference is not always turned
on. The reference is on during the following situations:
1.When the BOD is enabled (by programming the BODEN fuse).
2.When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR).
3.When the ADC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power consumption in power down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering power down mode.
Watchdog Timer
Table 20. Internal Voltage Reference Characteristics(1)
Symbol |
Parameter |
Condition |
Min |
Typ |
Max |
Units |
|
|
|
|
|
|
|
VBG |
Bandgap reference voltage |
TBD |
TBD |
1.23 |
TBD |
V |
tBG |
Bandgap reference start-up time |
TBD |
|
40 |
70 |
µs |
IBG |
Bandgap reference current |
TBD |
|
10 |
TBD |
µA |
consumption |
|
|||||
Note: 1. |
Values are guidelines only. Actual values are TBD. |
|
|
|
|
The Watchdog Timer is clocked from a separate on-chip oscillator which runs at 1 Mhz. This is the typical value at VCC = 5V. See characterization data for typical values at other
VCC levels. By controlling the Watchdog Timer prescaler, the Watchdog reset interval can be adjusted as shown in Table 22 on page 52. The WDR – Watchdog Reset –
instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is disabled and when a chip reset occurs. Eight different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog reset, the ATmega128 resets and executes from the Reset vector. For timing details on the Watchdog reset, refer to page 48.
To prevent unintentional disabling of the watchdog or unintentional change of time-out period, 3 different safety levels are selected by the Fuses M103C and WDTON as
shown in Table 21. Safety level 0 corresponds to the setting in ATmega103. There is no restriction on enabling the WDT in any of the safety levels. Refer to “Timed Sequences for Changing the Configuration of the Watch Dog Timer” on page 53 for details.
50 ATmega128(L)
2467B–09/01
ATmega128(L)
Table 21. WDT Configuration as a Function of the Fuse Settings of M103C and
WDTON.
|
|
|
|
|
How to |
|
|
Safety |
WDT Initial |
How to Disable |
Change |
M103C |
WDTON |
Level |
State |
the WDT |
Time-out |
|
|
|
|
|
|
Unprogrammed |
Unprogrammed |
1 |
Disabled |
Timed |
Timed |
|
|
|
|
sequence |
sequence |
|
|
|
|
|
|
Unprogrammed |
Programmed |
2 |
Enabled |
Always enabled |
Timed |
|
|
|
|
|
sequence |
|
|
|
|
|
|
Programmed |
Unprogrammed |
0 |
Disabled |
Timed |
No |
|
|
|
|
sequence |
restriction |
|
|
|
|
|
|
Programmed |
Programmed |
2 |
Enabled |
Always enabled |
Timed |
|
|
|
|
|
sequence |
|
|
|
|
|
|
Figure 27. Watchdog Timer
WATCHDOG
OSCILLATOR
Watchdog Timer Control
Register – WDTCR
2467B–09/01
Bit |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
|
– |
– |
– |
WDCE |
WDE |
WDP2 |
WDP1 |
WDP0 |
WDTCR |
|
|
|
|
|
|
|
|
|
|
Read/Write |
R |
R |
R |
R/W |
R/W |
R/W |
R/W |
R/W |
|
Initial value |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
• Bits 7..5 - Res: Reserved Bits
These bits are reserved bits in the ATmega128 and will always read as zero.
• Bit 4 - WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the watchdog will not be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the description of the WDE bit for a watchdog disable procedure. In
Safety Level 1 and 2, this bit must also be set when changing the prescaler bits. See “Timed Sequences for Changing the Configuration of the Watch Dog Timer” on page 53.
• Bit 3 - WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit has logic level one. To disable an enabled watchdog timer, the following procedure must be followed:
51
1.In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE even though it is set to one before the disable operation starts.
2.Within the next four clock cycles, write a logic 0 to WDE. This disables the watchdog.
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm described above. See “Timed Sequences for Changing the Configuration of the Watch Dog Timer” on page 53.
• Bits 2..0 - WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0
The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the
Watchdog Timer is enabled. The different prescaling values and their corresponding
Timeout Periods are shown in Table 22.
Table 22. Watchdog Timer Prescale Select(1)
|
|
|
|
Number of WDT |
Typical Time-out |
Typical Time-out |
WDP2 |
|
WDP1 |
WDP0 |
Oscillator Cycles |
at VCC = 3.0V |
at VCC = 5.0V |
0 |
|
0 |
0 |
16K |
TBD |
16 ms |
|
|
|
|
|
|
|
0 |
|
0 |
1 |
32K |
TBD |
32 ms |
|
|
|
|
|
|
|
0 |
|
1 |
0 |
64K |
TBD |
64 ms |
|
|
|
|
|
|
|
0 |
|
1 |
1 |
128K |
TBD |
0.13 s |
|
|
|
|
|
|
|
1 |
|
0 |
0 |
256K |
TBD |
0.26 s |
|
|
|
|
|
|
|
1 |
|
0 |
1 |
512K |
TBD |
0.5 s |
|
|
|
|
|
|
|
1 |
|
1 |
0 |
1,024K |
TBD |
1.0 s |
|
|
|
|
|
|
|
1 |
|
1 |
1 |
2,048K |
TBD |
2.0 s |
|
|
|
|
|
|
|
Note: |
1. Values are guidelines only. Actual values are TBD. |
|
The following code example shows one assembly and one C function for turning off the WDT. The example assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these functions.
Assembly Code Example
WDT_off:
; Write logical one to WDCE and WDE ldi r16, (1<<WDCE)|(1<<WDE) out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE) out WDTCR, r16
ret
C Code Example
void WDT_off(void)
{
/* Write logical one to WDCE and WDE */ WDTCR = (1<<WDCE) | (1<<WDE);
/* Turn off WDT */ WDTCR = 0x00;
}
52 ATmega128(L)
2467B–09/01