at90ls8535-8mi ATMEL Corporation, at90ls8535-8mi Datasheet - Page 74

• Manufacturer Part Number: at90ls8535-8mi
• Description: 8-bit Microcontroller With 8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Scanning Multiple
Channels
ADC Noise Canceling
Techniques
74
AT90S/LS8535
• ADC9..0: ADC Conversion result
These bits represent the result from the conversion. $000 represents analog ground and
$3FF represents the selected reference voltage minus one LSB.
Since change of analog channel always is delayed until a conversion is finished, the
Free Running Mode can be used to scan multiple channels without interrupting the con-
verter. Typically, the ADC Conversion Complete interrupt will be used to perform the
channel shift. However, the user should take the following fact into consideration: The
interrupt triggers once the result is ready to be read. In Free Running Mode, the next
conversion will start immediately when the interrupt triggers. If ADMUX is changed after
the interrupt triggers, the next conversion has already started and the old setting is
used.
Digital circuitry inside and outside the AT90S8535 generates EMI that might affect the
accuracy of analog measurements. If conversion accuracy is critical, the noise level can
be reduced by applying the following techniques:
1. The analog part of the AT90S8535 and all analog components in the application
2. Keep analog signal paths as short as possible. Make sure analog tracks run over
3. The AV
4. Use the ADC noise canceler function to reduce induced noise from the CPU.
5. If some Port A pins are used as digital outputs, it is essential that these do not
Figure 50. ADC Power Connections
should have a separate analog ground plane on the PCB. This ground plane is
connected to the digital ground plane via a single point on the PCB.
the analog ground plane and keep them well away from high-speed switching
digital tracks.
voltage via an LC network as shown in Figure 50.
switch while a conversion is in progress.
CC
pin on the AT90S8535 should be connected to the digital V
1
44
43
42
41
40
39
38
37
36
35
34
33
32
PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AGND
AVCC
PC0
CC
supply
1041H–11/01