18
32142DS–06/2013
ATUC64/128/256L3/4U
Note: 1. See Section 6. on page 40
3.4 I/O Line Considerations
3.4.1 JTAG Pins
The JTAG is enabled if TCK is low while the RESET_N pin is released. The TCK, TMS, and TDI
pins have pull-up resistors when JTAG is enabled. The TCK pin always has pull-up enabled dur-
ing reset. The TDO pin is an output, driven at VDDIO, and has no pull-up resistor. The JTAG
pins can be used as GPIO pins and multiplexed with peripherals when the JTAG is disabled.
Please refer to Section 3.2.3 on page 13 for the JTAG port connections.
3.4.2 PA00
Note that PA00 is multiplexed with TCK. PA00 GPIO function must only be used as output in the
application.
3.4.3 RESET_N Pin
The RESET_N pin is a schmitt input and integrates a permanent pull-up resistor to VDDIN. As
the product integrates a power-on reset detector, the RESET_N pin can be left unconnected in
case no reset from the system needs to be applied to the product.
The RESET_N pin is also used for the aWire debug protocol. When the pin is used for debug-
ging, it must not be driven by external circuitry.
3.4.4 TWI Pins PA21/PB04/PB05
When these pins are used for TWI, the pins are open-drain outputs with slew-rate limitation and
inputs with spike filtering. When used as GPIO pins or used for other peripherals, the pins have
the same characteristics as other GPIO pins. Selected pins are also SMBus compliant (refer to
Section on page 10). As required by the SMBus specification, these pins provide no leakage
path to ground when the ATUC64/128/256L3/4U is powered down. This allows other devices on
the SMBus to continue communicating even though the ATUC64/128/256L3/4U is not powered.
After reset a TWI function is selected on these pins instead of the GPIO. Please refer to the
GPIO Module Configuration chapter for details.
MSEO1 - MSEO0 Trace Frame Control Output
EVTI_N Event In Input Low
EVTO_N Event Out Output Low
General Purpose I/O pin
PA22 - PA00 Parallel I/O Controller I/O Port 0 I/O
PB27 - PB00 Parallel I/O Controller I/O Port 1 I/O
Table 3-8. Signal Description List, Continued
Signal Name Function Type
Active
Level Comments