Chapter 13: IEEE 1149.1 (JTAG) Boundary-Scan Testing for MAX II Devices
13–15
I/O Voltage Support in JTAG Chain
I/O Voltage Support in JTAG Chain
There can be several different Altera or non-Altera devices in a JTAG chain. However,
you should be cautious if the chain contains devices that have different VCCIO levels.
The TDOpin of a device drives out at the voltage level according to the VCCIO of the
device. For MAX II devices, the TDOpin will drive out at the voltage level according
to the VCCIO of I/O Bank 1. The devices can interface with each other although they
might have different VCCIO levels. For example, a device with 3.3-V VCCIO can drive to a
device with 5.0-V VCCIO because 3.3 V meets the minimum VIH on TTL-level input for
the 5.0-V VCCIO device. JTAG pins on MAX II devices can support 1.5-, 1.8-, 2.5-, or
3.3-V input levels, depending on the VCCIO voltage of I/O Bank 1.
f
Refer to the MAX II Architecture chapter in the MAX II Device Handbook for more
information on MultiVoltTM I/O support.
You can interface the TDIand TDOlines of the JTAG pins of devices that have
different VCCIO levels by inserting a level shifter between the devices. If possible, the
JTAG chain should be built such that a device with a higher VCCIO level drives to a
device with an equal or lower VCCIO level. By building the JTAG chain in this manner, a
level shifter may be required only to shift the TDOlevel to a level acceptable to the
JTAG tester. Figure 13–13 shows the JTAG chain of mixed voltages and how a level
shifter is inserted in the chain.
Figure 13–13. JTAG Chain of Mixed Voltages
Must be 5.0-V
Tolerant
Must be 3.3-V
Tolerant
TDI
5.0-V
3.3-V
2.5-V
V
V
V
CCIO
CCIO
CCIO
Tester
TDO
Level
1.5-V
1.8-V
Shifter
V
V
CCIO
CCIO
Shift TDO to Level
Accepted by Tester
if Necessary
Must be 1.8-V
Tolerant
Must be 2.5-V
Tolerant
BST for Programmed Devices
For a programmed device, the input buffers are turned off by default for I/O pins that
are set as output only in the design file. You cannot sample on the programmed device
output pins with the default BSDL file when the input buffers are turned off. You can
set the Quartus II software to always enable the input buffers on a programmed
device so it behaves the same as an unprogrammed device for boundary-scan testing,
allowing sample function on output pins in the design. This aspect can cause slight
increase in standby current as the unused input buffer is always on.
1. On the Assignments menu, click Settings.
2. Under Category, select Assembler.
3. Turn on Always Enable Input Buffers.
© October 2008 Altera Corporation
MAX II Device Handbook
ALTERA [ ALTERA CORPORATION ]
