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2.21
Boundary Scan
IEEE 1149.1 compliant JTAG is provided with the EP7312. Table 24 shows what JTAG instructions are
supported in the EP7312.
Instruction
Code
Description
EXTEST
0000
Places the selected
scan chain in test
mode.
SCAN_N
0010
Connects the Scan
Path Register between
TDI and TDO
SAMPLE / PRELOAD
0011
NOTE: This instruction is included for
product testing only
and should never be
used.
IDCODE
1110
Connects the ID register between TDI and
TDO
BYPASS
1111
Connects a 1-bit shift
register bit TDI and
TDO
Table 24. Instructions Supported in JTAG Mode
Note:
The INTEST function will not be supported for the EP7312.
Additional user-defined instructions exist, but these are not relevant to board-level testing. For further information please refer to the ARM DDI 0087E ARM720T Data Sheet.
As there are additional scan-chains within the ARM720T processor, it is necessary to include a scan-chain
select function — shown as SCAN_N in Table 24. To select a particular scan chain, this function must be
input to the TAP controller, followed by the 4-bit scan chain identification code. The identification code
for the boundary scan chain is 0011.
Note that it is only necessary to issue the SCAN_N instruction if the device is already in the JTAG mode.
The boundary scan chain is selected as the default on test-logic reset and any of the system resets.
The contents of the device ID-register for the EP7312 are shown in Figure 12. This is equivalent to
0x0F0F.0F0F. Note this is the ID-code for the ARM720T processor.
Version
0
0
0
Part number
0
1
1
1
1
0
0
0
0
1
1
Manufacturer ID
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Figure 12. Device ID Register
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