ATMEGA128A-AU Просмотр технического описания (PDF) - Atmel Corporation

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ATMEGA128A-AU

8-Bit AVR Microcontroller with 128K Bytes In-System Programmable Flash

Atmel Corporation 

ATmega128A

9. Errata

The revision letter in this section refers to the revision of the ATmega128A device.

9.1 ATmega128A Rev. U

• Wrong value for Version in the JTAG Device Identification Register

• First Analog Comparator conversion may be delayed

• Interrupts may be lost when writing the timer registers in the asynchronous timer

• Stabilizing time needed when changing XDIV Register

• Stabilizing time needed when changing OSCCAL Register

• IDCODE masks data from TDI input

• Reading EEPROM by using ST or STS to set EERE bit triggers unexpected interrupt request

1. First Analog Comparator conversion may be delayed

If the device is powered by a slow rising VCC, the first Analog Comparator conversion will

take longer than expected on some devices.

Problem Fix/Workaround

When the device has been powered or reset, disable then enable the Analog Comparator

before the first conversion.

2. Interrupts may be lost when writing the timer registers in the asynchronous timer

The interrupt will be lost if a timer register that is synchronous timer clock is written when the

asynchronous Timer/Counter register (TCNTx) is 0x00.

Problem Fix/Workaround

Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor

0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous

Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).

3. Stabilizing time needed when changing XDIV Register

After increasing the source clock frequency more than 2% with settings in the XDIV register,

the device may execute some of the subsequent instructions incorrectly.

Problem Fix / Workaround

The NOP instruction will always be executed correctly also right after a frequency change.

Thus, the next 8 instructions after the change should be NOP instructions. To ensure this,

follow this procedure:

1.Clear the I bit in the SREG Register.

2.Set the new pre-scaling factor in XDIV register.

3.Execute 8 NOP instructions

4.Set the I bit in SREG

This will ensure that all subsequent instructions will execute correctly.

Assembly Code Example:

CLI

OUT XDIV, temp

NOP

NOP

NOP

; clear global interrupt enable

; set new prescale value

; no operation

; no operation

; no operation

19

8151GS–AVR–07/10

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