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.