ATMEGA1284-PU Atmel, ATMEGA1284-PU Datasheet - Page 256
![IC MCU AVR 128K FLASH 40PDIP](/photos/6/70/67049/453-40-dip_sml.jpg)
ATMEGA1284-PU
Manufacturer Part Number
ATMEGA1284-PU
Description
IC MCU AVR 128K FLASH 40PDIP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA1284-PU
Core Processor
AVR
Core Size
8-Bit
Speed
20MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
32
Program Memory Size
128KB (64K x 16)
Program Memory Type
FLASH
Eeprom Size
4K x 8
Ram Size
16K x 8
Voltage - Supply (vcc/vdd)
1.8 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)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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22.9
22.9.1
8272A–AVR–01/10
Register Description
ADMUX – ADC Multiplexer Selection Register
Example:
ADMUX = 0xED (ADC3 - ADC2, 10x gain, 2.56V reference, left adjusted result)
Voltage on ADC3 is 300 mV, voltage on ADC2 is 500 mV.
ADCR = 512 * 10 * (300 - 500) / 2560 = -400 = 0x270
ADCL will thus read 0x00, and ADCH will read 0x9C. Writing zero to ADLAR right adjusts the
result: ADCL = 0x70, ADCH = 0x02.
• Bit 7:6 – REFS1:0: Reference Selection Bits
These bits select the voltage reference for the ADC, as shown in
changed during a conversion, the change will not go in effect until this conversion is complete
(ADIF in ADCSRA is set). The internal voltage reference options may not be used if an external
reference voltage is being applied to the AREF pin.
Table 22-3.
Note:
• Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing the
ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing conver-
sions. For a complete description of this bit, see
page
• Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC.
These bits also select the gain for the differential channels. See
details. If these bits are changed during a conversion, the change will not go in effect until this
conversion is complete (ADIF in ADCSRA is set).
164A/164PA/324A/324PA/644A/644PA/1284/1284P
Bit
(0x7C)
Read/Write
Initial Value
REFS1
0
0
1
1
259.
If differential channels are selected, only 2.56V should be used as Internal Voltage Reference.
REFS0
Voltage Reference Selections for ADC
REFS1
0
1
0
1
R/W
7
0
Voltage Reference Selection
AREF, Internal Vref turned off
AVCC with external capacitor at AREF pin
Internal 1.1V Voltage Reference with external capacitor at AREF pin
Internal 2.56V Voltage Reference with external capacitor at AREF pin
REFS0
R/W
6
0
ADLAR
R/W
5
0
MUX4
R/W
4
0
”ADCL and ADCH – The ADC Data Register” on
MUX3
R/W
3
0
MUX2
R/W
2
0
Table 22-4 on page 257
Table
MUX1
R/W
1
0
22-3. If these bits are
MUX0
R/W
0
0
ADMUX
256
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