OLIMEX© 2015
A20-SOM user's manual
6.7 Jumper description
Please note that two jumpers on the board are SMT type. If you feel insecure of your
soldering/cutting technique it is better not to try to adjust the jumpers since it is possible to damage
the board.
Board jumpers
Jumper name
Type
Default position
Function
NAND_E
SMT
Either CLOSED or
OPEN, depending
whether the board
has 4GB NAND
MEMORY MODULE
Controls whether the NAND memory
module is enabled or disabled.
If the jumper is closed than the
NAND memory is operational.
By default it should be set
properly for your board.
5V_E
SMT
OPEN
The jumper is used for internal
testing. It is not recommended to
change its position. When the
jumper is closed it removes a
circuit that handles cases in which
you prove power supply to both +5V
and 5VEXT power lines.
6.8 Additional hardware components
The components below are mounted on the A20-SOM but are not discussed above. They are listed
here for completeness:
Reset button –
used to reset the board
Power button –
used to power up the board
Recovery button –
used to wake-up the board (from power down state)
1GB = 2×[4Gb (256 M x 16 bit) DDR3 SDRAM] –
the exact memory used currently is
SAMSUNG K4B4G1646D-BCK0 – the memory clock in board revisions A and B of A20-SOM
was 384MHz; the memory clock in hardware revisions C, D and newer ones is improved to
480MHz
The DDR3 memory part name in the schematic might be outdated. We have used a number of
different but fully compatible DDR3 memories due to supply unavailability. It is always
recommended to check the exact memory name printed on the component itself.
4GB = 1×[32Gb (4096 M x 8 bit) NAND FLASH]
– only available on the 4GB version of the
board; the exact memory used in the board revision mentioned is HYNIX H27UBG8T2A
PWR_LED – turns on upon powering the board
CHGLED – lights when charging a battery connected to the Li-Po battery connector.
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