EP3C16F256I7N Altera, EP3C16F256I7N Datasheet - Page 393

• Manufacturer Part Number: EP3C16F256I7N
• Description: Cyclone III
• Manufacturer: Altera

I/O Voltage
Support in JTAG
Chain
Altera Corporation-Preliminary
March 2007
f
1
CONFIG_IO Instruction Mode
The CONFIG_IO instruction allows you to perform I/O reconfiguration
through JTAG ports using the I/O configuration shift register (IOCSR).
IOCSR is a chain of I/O element (IOE) registers, which contains
configuration bits to control the IOE characteristics. Thus, you can
perform I/O reconfiguration by shifting new configuration data into the
IOCSR. CONFIG_IO instruction needs to be used together with
ACTIVE_DISENGAGE instruction to interrupt active configuration.
CONFIG_IO also drives the nSTATUS pin low and releases it when the
CONFIG_IO instruction is no longer active.
1
A JTAG chain can contain several different devices. However, you should
be cautious if the chain contains devices that have different V
The output voltage level of the TDO pin must meet the specifications of
the TDI pin it drives. For Cyclone III devices, the TDO pin is powered by
the V
drives out 3.3 V.
Devices can interface with each other although they might have different
V
device with a 5.0-V TDI pin because 3.3 V meets the minimum TTL-level
V
2.5-V or 3.3-V input levels.
1
For more information on MultiVolt™ I/O support, see the Cyclone III
Device I/O Feature chapter of the Cyclone III Device Handbook.
You can also interface the TDI and TDO lines of the devices that have
different V
possible, the JTAG chain should be built such that a device with a higher
V
way, a level shifter may be required only to shift the TDO level to a level
acceptable to the JTAG tester.
mixed voltages and how a level shifter is inserted in the chain.
CCIO
IH
CCIO
for the 5.0-V TDI pin. JTAG pins on Cyclone III devices can support
CCIO
levels. For example, a device with a 3.3-V TDO pin can drive to a
level drives to a device with an equal or lower V
If you are testing after configuring the device, the
programmable weak pull-up resistor or the bus hold feature
overrides the HIGHZ value at the pin.
The nCONFIG pin must not be low and nSTATUS pin must go
high before you can issue the CONFIG_IO instruction.
For multiple devices in a JTAG chain with 3.0-V/ 3.3-V I/O
standard, you need to connect a 25 Ω series resistor on a TDO pin
driving a TDI pin.
power supply. Since the V
CCIO
levels by inserting a level shifter between the devices. If
Figure 14–13
Cyclone III Device Handbook, Volume 1
CCIO
I/O Voltage Support in JTAG Chain
supply is 3.3 V, the TDO pin
shows the JTAG chain of
CCIO
level. This
CCIO
levels.
14–19