261
2467S–AVR–07/09
ATmega128
Scanning the ADC
shows a block diagram of the ADC with all relevant control and observe signals. The
is attached to each of these signals. The ADC need not be
used for pure connectivity testing, since all analog inputs are shared with a digital port pin as
well.
Figure 131.
Analog to Digital Converter
The signals are described briefly in
Table 103.
Boundary-scan Signals for the Analog Comparator
Signal
Name
Direction as
Seen from the
Comparator
Description
Recommended
Input when not
in Use
Output values when
Recommended
Inputs are Used
AC_IDLE
Input
Turns off Analog
comparator when
true
1
Depends upon µC
code being executed
ACO
Output
Analog
Comparator
Output
Will become
input to µC code
being executed
0
ACME
Input
Uses output
signal from ADC
mux when true
0
Depends upon µC
code being executed
ACBG
Input
Bandgap
Reference enable
0
Depends upon µC
code being executed
10-bit DAC
+
-
AREF
PRECH
DACOUT
COMP
MUXEN_7
ADC_7
MUXEN_6
ADC_6
MUXEN_5
ADC_5
MUXEN_4
ADC_4
MUXEN_3
ADC_3
MUXEN_2
ADC_2
MUXEN_1
ADC_1
MUXEN_0
ADC_0
NEGSEL_2
ADC_2
NEGSEL_1
ADC_1
NEGSEL_0
ADC_0
EXTCH
+
-
+
-
10x
20x
G10
G20
ST
ACLK
AMPEN
2.56V
ref
IREFEN
AREF
VCCREN
DAC_9..0
ADCEN
HOLD
PRECH
GNDEN
PASSEN
ACTEN
COMP
SCTEST
ADCBGEN
To Comparator
1.22V
ref
AREF