SAM3U Datasheet, PDF (24/59 Pages) ATMEL Corporation – AT91SAM ARM-based Flash MCU

6. Input/Output Lines
The SAM3U has different kinds of input/output (I/O) lines, such as general purpose I/Os (GPIO)
and system I/Os. GPIOs can have alternate functions thanks to multiplexing capabilities of the
PIO controllers. The same GPIO line can be used whether it is in IO mode or used by the multi-
plexed peripheral. System I/Os are pins such as test pin, oscillators, erase pin, analog inputs or
debug pins.
With a few exceptions, the I/Os have input schmitt triggers. Refer to the footnotes associated
with “PIO Controller - PIOA - PIOB - PIOC” on page 6 within Table 3-1, “Signal Description List”.
6.1 General Purpose I/O Lines (GPIO)
GPIO Lines are managed by PIO Controllers. All I/Os have several input or output modes such
as, pull-up, input schmitt triggers, multi-drive (open-drain), glitch filters, debouncing or input
change interrupt. Programming of these modes is performed independently for each I/O line
through the PIO controller user interface. For more details, refer to the “PIO Controller” section
of the product datasheet.
The input output buffers of the PIO lines are supplied through VDDIO power supply rail.
The SAM3U embeds high speed pads able to handle up to 65 MHz for HSMCI and SPI clock
lines and 35 MHz on other lines. See “AC Characteristics” of the product datasheet for more
details. Typical pull-up value is 100 kΩ for all I/Os.
Each I/O line also embeds an ODT (On-Die Termination), (see Figure 6-1 below). ODT consists
of an internal series resistor termination scheme for impedance matching between the driver
output (SAM3) and the PCB track impedance preventing signal reflection. The series resistor
helps to reduce I/Os switching current (di/dt) thereby reducing in turn, EMI. It also decreases
overshoot and undershoot (ringing) due to inductance of interconnect between devices or
between boards. In conclusion, ODT helps reducing signal integrity issues.
Figure 6-1. On-Die Termination schematic
ODT
36 Ohms Typ.
Z0 ~ Zout + Rodt
Rodt
SAM3 Driver with
Zout ~ 10 Ohms
PCB Trace
Z0 ~ 50 Ohms
Receiver
6.2 System I/O Lines
System I/O lines are pins used by oscillators, test mode, reset, flash erase and JTAG to name
but a few.
6.3 Serial Wire JTAG Debug Port (SWJ-DP)
The SWJ-DP pins are TCK/SWCLK, TMS/SWDIO, TDO/SWO, TDI and commonly provided on
a standard 20-pin JTAG connector defined by ARM. For more details about voltage reference
and reset state, refer to Table 3-1, “Signal Description List”
24 SAM3U Series
6430ES–ATARM–22-Aug-11