253
ATmega64A [DATASHEET]
8160D–AVR–02/2013
As an example, consider the task of verifying a 1.5V ±5% input signal at ADC channel 3 when the power supply is
5.0V and AREF is externally connected to V
CC.
The recommended values from
Table 26-5 are used unless other values are given in the algorithm in
Table 26-6.Only the DAC and Port Pin values of the Scan-chain are shown. The column “Actions” describes what JTAG
instruction to be used before filling the Boundary-scan Register with the succeeding columns. The verification
should be done on the data scanned out when scanning in the data on the same row in the table.
Note:
1. Using this algorithm, the timing constraint on the HOLD signal constrains the TCK clock frequency. As the algorithm keeps
HOLD high for five steps, the TCK clock frequency has to be at least five times the number of scan bits divided by the maxi-
mum hold time, thold,max.
26.6
ATmega64A Boundary-scan Order
Table 26-7 shows the Scan order between TDI and TDO when the Boundary-scan Chain is selected as data path.
Bit 0 is the LSB; the first bit scanned in, and the first bit scanned out. The scan order follows the pinout order as far
as possible. Therefore, the bits of Port A are scanned in the opposite bit order of the other ports. Exceptions from
the rules are the scan chains for the analog circuits, which constitute the most significant bits of the scan chain
regardless of which physical pin they are connected to. In
Figure 26-3, PXn, Data corresponds to FF0, PXn. Con-
trol corresponds to FF1, and PXn. Pullup_enable corresponds to FF2. Bit 2, 3, 4, and 5 of Port C is not in the scan
chain, since these pins constitute the TAP pins when the JTAG is enabled.
The lower limit is:
1024 1.5
V 0,95 5V
291
0x123
==
The upper limit is:
1024 1.5
V 1.05 5V
323
0x143
==
Table 26-6.
Algorithm for Using the AD
CSte
p
Actions
ADCEN
DAC
MUXEN
HOLD
PRECH
PA3.
Data
PA3.
Control
PA3.
Pull-
up_
Enable
1
SAMPLE_PRELOAD
1
0x200
0x08
1
0
2
EXTEST
1
0x200
0x08
0
1
0
3
1
0x200
0x08
1
0
4
1
0x123
0x08
1
0
5
1
0x123
0x08
1
0
6
Verify the COMP bit scanned out to be 0
1
0x200
0x08
1
0
7
1
0x200
0x08
0
1
0
8
1
0x200
0x08
1
0
9
1
0x143
0x08
1
0
10
1
0x143
0x08
1
0
11
Verify the COMP bit scanned out to be 1
1
0x200
0x08
1
0