11–4
Chapter 11: In-System Programmability Guidelines for MAX II Devices
IEEE Std. 1149.1 Signals
Pull-Up and Pull-Down of JTAG Pins During In-System Programming
A MAX II device operating in in-system programming mode requires four pins:
TDI,
TDO, TMS,
and
TCK.
The detailed description and function of each pin can be found in
the
chapter in the
MAX II
Device Handbook.
Three of the four JTAG pins have internal weak pull-up or pull-down resistors. The
TDI
and
TMS
pins have internal weak pull-up resistors while the
TCK
pin has an
internal weak pull-down resistor. However, for device programming in a JTAG chain,
there might be devices that do not have internal pull-up or pull-down resistors. Altera
recommends to externally pull TMS high through 10-kΩ and
TCK
low through 1-kΩ
resistors. Pulling-up the
TDI
signal externally for the MAX II device is optional.
shows the external pull-up and pull-down for
TMS
and
TCK
of the JTAG
chain. The
TDO
pin does not have internal pull-up or pull-down resistors, and does
not require external pull-up or pull-down resistors.
Figure 11–1.
External Pull-Up and Pull-Down Resistors for TMS and TCK of a JTAG Chain
10-Pin Male Header
(Top View)
VCC
VCC
10 kΩ
MAX II Device
TDI
TMS
TDO
TCK
Other ISP-Capable
Device
TDI
TMS
TDO
TCK
Other ISP-Capable
Device
TDI
TMS
TDO
TCK
GND
1kΩ
The
TMS
pin is pulled high so that the TAP controller will remain in the
TEST_LOGIC/RESET
state even if there is input from
TCK.
To prevent
TCK
from
pulsing high, the
TCK
pin is pulled low during power-up. Pulling
TCK
high is not
recommended because an increase in the power supply to the pull-up resistor causes
the
TCK
to pulse high; thus, it is possible for the TAP controller to reach an unintended
state.
IEEE Std. 1149.1 Signals
This section provides guidelines for programming with the IEEE Std. 1149.1 (JTAG) interface.
TCK Signal
Most in-system programming failures are caused by a noisy
TCK
signal. Noisy
transitions on rising or falling edges can cause incorrect clocking of the IEEE Std.
1149.1 Test Access Port (TAP) controller. Incorrect clocking can cause the state
machine to transition to an unknown state, leading to in-system programming
failures.
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