ATMEGA16L_14 Datasheet, PDF (235/357 Pages) ATMEL Corporation – High Endurance Non-volatile Memory segments

ATmega16(L)
Figure 120. Boundary-scan Cells for Oscillators and Clock Options
XTAL1/TOSC1
XTAL2/TOSC2
ShiftDR
To
Next
Cell
EXTEST
Oscillator
0
1
0
DQ
DQ
1
G
ENABLE
OUTPUT
ShiftDR
To
Next
Cell
FF1
0
DQ
1
From ClockDR
Previous
Cell
UpdateDR
From
Previous
Cell
ClockDR
Table 90 summaries the scan registers for the external clock pin XTAL1, Oscillators with
XTAL1/XTAL2 connections as well as 32 kHz Timer Oscillator.
Table 90. Scan Signals for the Oscillators^(1)(2)(3)
Enable Signal Scanned Clock Line Clock Option
Scanned Clock Line
when not Used
EXTCLKEN
EXTCLK (XTAL1)
External Clock
0
OSCON
OSCCK
External Crystal
0
External Ceramic
Resonator
RCOSCEN
RCCK
External RC
1
OSC32EN
OSC32CK
Low Freq. External Crystal
0
TOSKON
TOSCK
32 kHz Timer Oscillator
0
Notes:
1. Do not enable more than one clock source as main clock at a time.
2. Scanning an Oscillator output gives unpredictable results as there is a frequency drift between
the Internal Oscillator and the JTAG TCK clock. If possible, scanning an external clock is
preferred.
3. The clock configuration is programmed by fuses. As a fuse is not changed run-time, the clock
configuration is considered fixed for a given application. The user is advised to scan the same
clock option as to be used in the final system. The enable signals are supported in the scan
chain because the system logic can disable clock options in sleep modes, thereby disconnect-
ing the Oscillator pins from the scan path if not provided. The INTCAP Fuses are not
supported in the scan-chain, so the boundary scan chain can not make a XTAL Oscillator
requiring internal capacitors to run unless the fuse is correctly programmed.
Scanning the Analog
Comparator
The relevant Comparator signals regarding Boundary-scan are shown in Figure 121. The
Boundary-scan cell from Figure 122 is attached to each of these signals. The signals are
described in Table 91.
The Comparator need not be used for pure connectivity testing, since all analog inputs are
shared with a digital port pin as well.
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