AT89LP3240 Atmel Corporation, AT89LP3240 Datasheet - Page 137

• Manufacturer Part Number: AT89LP3240
• Manufacturer: Atmel Corporation

Specifications of AT89LP3240

• Flash (kbytes): 32 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 38
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 153.8
• Sram (kbytes): 4.25
• Eeprom (bytes): 8192
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 3.6
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

20.3
20.4
3706C–MICRO–2/11
Clock Selection
Starting a Conversion
Figure 20-5. Equivalent Analog Output Model
The DADC requires a clock of 2 MHz or less to achieve full resolution. By default the DADC will
use an internal 2 MHz clock generated from the 8 MHz internal oscillator. The internal oscillator
will be enabled even if it is not supplying the system clock. This may result in higher power con-
sumption. Conversely, the DADC clock can be generated directly from the system clock using a
7-bit prescaler. The prescaler output is controlled by the ACK bits in DADC as shown in
20-6.
In ADC mode, there are no requirements on the clock frequency with respect to the system
clock. The ADC prescaler selection is independent of the system clock divider and the ADC may
operate at both higher or lower frequencies than the CPU. However, in DAC mode the ADC
clock frequency must not be higher than the CPU clock, including any clock division from the
system clock.
Figure 20-6. DADC Clock Selection
Setting the GO/BSY bit (DADC.6) when ADCE = 1 starts a single conversion in both ADC and
DAC modes. The bit remains set while the conversion is in progress and is cleared by hardware
when the conversion completes. The ADC channel should not be changed while a conversion is
in progress.
Alternatively, a conversion can be started automatically by various timer sources. Conversion
trigger sources are selected by the TRG bits in DADI. A conversion is started every time the
selected timer overflows, allowing for conversions to occur at fixed intervals. The GO/BSY bit will
INTERNAL
8MHz OSC
V
OUT
AV
ACK0
ACK1
ACK2
DD
/2
R
100 kΩ
CK
OUT
÷ 4
=
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
C
10 pF
PIN
AT89LP3240/6440
=
DAn
Figure
137