Atmel SAM4S Xplained Pro Starter Kit Atmel ATSAM4S-XSTK ATSAM4S-XSTK Data Sheet

 

Atmel SAM4S Xplained Pro [USER GUIDE]

Atmel-42075B-MCU-Atmel SAM4S Xplained Pro-USER GUIDE-03/2013

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The revision and product identifier of Xplained Pro boards can be found in two ways, through Atmel Studio or

by looking at the sticker on the bottom side of the PCB.
By connecting a Xplained Pro MCU board to a computer with Atmel Studio running, an information window will

pop up. The first 6 digits of the serial number, which is listed under kit details, contain the product identifier and

revision. Information about connected Xplained Pro extension boards will also appear in the Atmel Kits window.
The same information can be found on the sticker on the bottom side of the PCB. Most kits will print the

identifier and revision in plain text as A09-nnnn\rr where nnnn is the identifier and rr is the revision. Boards with

limited space have a sticker with only a QR-code which contains a serial number string.
The serial number string has the following format:

    "nnnnrrssssssssss"

    n = product identifier

    r = revision

    s = serial number

    

The kit identifier for SAM4S Xplained Pro is 1803.

On this revision, the SPI clock net is improved to reduce any issues that might be caused by reflections. The

SPI has been removed from the LCD (EXT4 connector) to reduce load on the clock net. The remaining clock

lines have been divided into four terminated nets for each SPI source (EXT1, EXT2, EXT3, and EDBG) and

routed in a star like layout. A series terminator resistor of 43ohm is placed on each clock net, close to the SPI

clock pin. This reduces any issues that might be caused by reflections comming back from unterminated/

unused clock lines. It also reduces the rise/fall time of the clock edges and that will also help to reduce any

reflection issues.

●

SAM4S has an on-die series termination of the SPI CLK which makes this signal not usable for a multi

drop clock distribution because all devices along the line will see a fraction of VCC until the signal is

reflected from the end of the transmission line. On the SAM4S Xplained Pro revision 4 this signal is

routed to each extension connector with EXT1 at the end of the line. That means extensions that are

connected along the transission line e.g. EXT3 header is likely to fail due to a non-monotinic edge caused

by relections and the fraction of VCC that is present for a short time until the reflection comes back from

the end of the line.

●

By slowing down the clock rise time with a capacitor, and thus effectively increasing the line length at

which point it becomes a transmission line, it is possible to remove the clock issue. A 56pF capacitor

has been mounted on the bottom side of the board between the SPI clock and GND. This however

reduces the maximum SPI clock speed and it is recommended to not run this faster than 30MHz (this

also depends on how much additional capacitance is added by connected extensions and needs to

be checked case by case). The capacitor was added on revision 4 on the bottom side of the EXT3

header.