ATMEGA640 datasheet(420/436 Pages) MICROCHIP

420 / 436 page

420

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

37.18 ATmega2561 rev. A

• Non-Read-While-Write area of flash not functional

• Part does not work under 2.4 Volts

• Incorrect ADC reading in differential mode

• Internal ADC reference has too low value

• IN/OUT instructions may be executed twice when Stack is in external RAM

• EEPROM read from application code does not work in Lock Bit Mode 3

Non-Read-While-Write area of flash not functional

The Non-Read-While-Write area of the flash is not working as expected. The problem is related to the speed of

the part when reading the flash of this area.

Problem Fix/Workaround

- Only use the first 248K of the flash.

- If boot functionality is needed, run the code in the Non-Read-While-Write area at maximum 1/4th of the max-

imum frequency of the device at any given voltage. This is done by writing the CLKPR register before entering

the boot section of the code.

2. Part does not work under 2.4 volts

The part does not execute code correctly below 2.4 volts.

Problem Fix/Workaround

Do not use the part at voltages below 2.4 volts.

3. Incorrect ADC reading in differential mode

The ADC has high noise in differential mode. It can give up to 7 LSB error.

Problem Fix/Workaround

Use only the 7 MSB of the result when using the ADC in differential mode.

4. Internal ADC reference has too low value

The internal ADC reference has a value lower than specified.

Problem Fix/Workaround

- Use AVCC or external reference.

- The actual value of the reference can be measured by applying a known voltage to the ADC when using the

internal reference. The result when doing later conversions can then be calibrated.

5. IN/OUT instructions may be executed twice when Stack is in external RAM

If either an IN or an OUT instruction is executed directly before an interrupt occurs and the stack pointer is

located in external ram, the instruction will be executed twice. In some cases this will cause a problem, for

example:

- If reading SREG it will appear that the I-flag is cleared.

- If writing to the PIN registers, the port will toggle twice.

- If reading registers with interrupt flags, the flags will appear to be cleared.

Problem Fix/Workaround

There are two application workarounds, where selecting one of them, will be omitting the issue:

- Replace IN and OUT with LD/LDS/LDD and ST/STS/STD instructions.

ATMEGA640 Datasheet(PDF) 420 Page - Microchip Technology

ATMEGA640 Datasheet(HTML) 420 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL