Underclocking SDRAM

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Underclocking SDRAM

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lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by MindBender on Wed Jul 15 05:58:16 MST 2015
The Embedded Artists LPC1788 board uses an IS42S32800B-7BL SDRAM chip, which is 256Mbit (8Mx32) in size and specifies a clock rate of 143MHz. However, the demo software that comes with the board sets CCLKSEL to 0x00000101 and EMCCLKSEL to 0x00000001, operating this SDRAM chip at 60MHz.

Is it safe/reliable to underclock SDRAM (that far)? If so, do we need to alter latencies to make sure it is still refreshed in time?

We found the IS42S32800B-7BL a bit too big/expensive for our own design, so we have found an alternative, but that one too is rated well over 60MHz.
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lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by mc on Wed Jul 15 09:45:19 MST 2015
Hi Mindebender,
SDRAM will work after programming it with correct timings viz CAS, refresh time etc.
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