Datasheet

29
11057BS–ATARM–13-Jul-12
SAM3X/A
29
11057BS–ATARM–13-Jul-12
SAM3X/A
6. Input/Output Lines
The SAM3X/A 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 PIO line can be used whether in IO mode or by the multiplexed
peripheral. System I/Os include pins such as test pins, oscillators, erase or analog inputs.
With a few exceptions, the I/Os have input schmitt triggers. Refer to the footnotes associated
with PIOA to PIOF on page 14, at the end of 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 SAM3X/A embeds high speed pads able to handle up to 65 MHz for HSMCI and SPI clock
lines and 45 MHz on other lines. See product AC Characteristics 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 IOs 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
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. Described below are the SAM3X/A system I/O lines shared with PIO lines.
These pins are software configurable as general purpose I/O or system pins. At startup, the
default function of these pins is always used.
PCB Trace
Z0 ~ 50 Ohms
Receiver
SAM3 Driver with
Rodt
Zout ~ 10 Ohms
Z0 ~ Zout + Rodt
ODT
36 Ohms Typ.