AT91SAM datasheet(26/67 Pages) ATMEL

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11100BS–ATARM–31-Jul-12

SAM4S Series [Preliminary]

Input/Output Lines

The SAM4S has several kinds of input/output (I/O) lines such as general purpose I/Os (GPIO)

and system I/Os. GPIOs can have alternate functionality due to multiplexing capabilities of the

PIO controllers. The same PIO line can be used whether in I/O mode or by the multiplexed

peripheral. System I/Os include pins such as test pins, oscillators, erase or analog inputs.

6.1

General Purpose I/O Lines

GPIO Lines are managed by PIO Controllers. All I/Os have several input or output modes such

as pull-up or pull-down, 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 product “PIO Control-

ler” section.

The input/output buffers of the PIO lines are supplied through VDDIO power supply rail.

The SAM4S embeds high speed pads able to handle up to 70 MHz for HSMCI (MCK/2), 70 MHz

for SPI clock lines and 46 MHz on other lines. See the “AC Characteristics” sub-section of the

product Electrical Characteristics. Typical pull-up and pull-down value is 100 k

Ω for all I/Os.

Each I/O line also embeds an ODT (On-Die Termination), (see Figure 6-1 below). It consists of

an internal series resistor termination scheme for impedance matching between the driver out-

put (SAM4S) and the PCB trace 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 diminish 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 and JTAG to name but a few.

Described below in Table 6-1 are the SAM4S 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

SAM4 Driver with

Rodt

Zout ~ 10 Ohms

Z0 ~ Zout + Rodt

ODT

36 Ohms Typ.

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