AT89LP51ED2-20AAU Atmel, AT89LP51ED2-20AAU Datasheet - Page 168

• Manufacturer Part Number: AT89LP51ED2-20AAU
• Description: 8-bit Microcontrollers - MCU 64KB 20MHz 2.4V-5.5V
• Manufacturer: Atmel

Specifications of AT89LP51ED2-20AAU

• Rohs: yes
• Core: 8051
• Processor Series: AT89x
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 20 MHz
• Program Memory Size: 64 KB
• Data Ram Size: 256 B
• On-chip Adc: Yes
• Operating Supply Voltage: 2.4 V to 5.5 V
• Operating Temperature Range: - 40 C to + 85 C
• Package / Case: LQFP-44
• Mounting Style: SMD/SMT
• Data Rom Size: 4 KB
• Interface Type: 2-Wire, SPI, UART
• Number Of Programmable I/os: 36
• Number Of Timers: 3
• Program Memory Type: Flash
• Factory Pack Quantity: 160

21.1
168
ADC Operation
AT89LP51RD2/ED2/ID2 Preliminary
Table 21-1.
The ADC converts an analog input voltage to a 10-bit signed digital value through successive
approximation. When DIFF (DADI.3) is zero, the ADC operates in single-ended mode and the
input voltage is the difference between the voltage at the input pin and V
mode (DIFF = 1) the input voltage is the difference between the positive and negative input pins.
The minimum value represents zero difference and the maximum values represent a difference
of positive or negative V
The analog input channel is selected by writing to the ACS bits in DADI. The first six Port 0 input
pins can be selected as single-ended inputs to the ADC. Three pairs of Port 0 pins can be
selected as differential inputs.The ACON bit (DADI.7) must be set to one to connect the input
pins to the ADC. Prior to changing ACS, ACON must be cleared to zero. This ensures that
crosstalk between channels is limited. ACON must be set back to one after ACS is updated.
ACON and ACS should not be changed while a conversion is in progress. ADC input channels
must have their port pins configured for input-only mode. The AT89LP51RD2/ED2/ID2 also
includes an on-chip temperature sensor and voltage supply channel. These features are
available when ACS = 6. See
The equivalent model for the analog input circuitry is illustrated in
applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of
whether that channel is selected as input to the ADC. When the channel is selected, the source
must drive the S/H capacitor through the series resistance (combined resistance in the input
path). To achieve 10-bit resolution the S/H capacitor must be charged to within 1/2 LSB of the
expected value within the 1 ADC clock period sample time. High impedance sources may
require a reduction in the ADC clock frequency to achieve full resolution.
Figure 21-2. Equivalent Analog Input Model
The ADC is enabled by setting the ADCE bit in DADC. Some settling time is required for the ref-
erence circuits to stabilize after the ADC is enabled. The ADC does not consume power when
ADCE is cleared, so it is recommended to switch off the ADC before entering power saving
modes.
Right Adjust
01FFh
FF00h
FE01h
0100h
0
ADCn
Example ADC Conversion Codes
Left Adjust
7FC0h
C000h
4000h
8040h
C
10 pF
0
PIN
REF
=
minus 1 LSB.
Section
Single-Ended Mode (V
V
V
DD
DD
V
V
21.2.
/2 + 511/512 x V
/2 – 511/512 x V
DD
DD
/2 + 1/2 x V
/2 – 1/2 x V
10 kΩ
R
V
DD
IN
/2
=
REF
REF
REF
REF
IN
)
R
10 kΩ
MUX
Differential Mode (V
Figure
=
–511/512 x V
511/512 x V
21-2. An analog source
–1/2 x V
1/2 x V
C
2 pF
DD
S/H
0
/2. In differential
=
REF
3714A–MICRO–7/11
REF
REF
REF
IN
+ – V
IN
-)