Samsung S5PC110, Manual

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S5PC110_UM 7 SD/MMC CONTROLLER
7-58
7.10.8 CLOCK CONTROL REGISTER
7.10.8.1 Command Register
•
CLKCON0, R/W, Address = 0xEB00_002C
•
CLKCON1, R/W, Address = 0xEB10_002C
•
CLKCON2, R/W, Address = 0xEB20_002C
•
CLKCON3, R/W, Address = 0xEB30_002C
At the initialization of the Host Controller, the Host Driver sets the SDCLK Frequency Select according to the
Capabilities register.
CLKCON Bit Description Initial State
SELFREQ [15:8] SDCLK Frequency Select
This register is used to select the frequency of SDCLK pin. The
frequency is not programmed directly; rather this register holds
the divisor of the Base Clock Frequency For SD Clock in the
Capabilities register. Only the following settings are allowed.
80h base clock divided by 256
40h base clock divided by 128
20h base clock divided by 64
10h base clock divided by 32
08h base clock divided by 16
04h base clock divided by 8
02h base clock divided by 4
01h base clock divided by 2
00h base clock (10MHz-63MHz)
Setting 00h specifies the highest frequency of the SD Clock.
Setting multiple bits, the most significant bit is used as the
divisor. But multiple bits must not be set. The two default divider
values are calculated by the frequency that is defined by the
Base Clock Frequency For SD Clock in the Capabilities register.
(1) 25MHz divider value,
(2) 400kHz divider value
According to the SD Physical Specification Version 1.01 and the
SDIO Card Specification Version 1.0, maximum SD Clock
frequency is 25MHz, and never exceeds this limit.
The frequency of SDCLK is set by the following formula:
Clock Frequency = (Base Clock)/ divisor
Therefore, select the smallest possible divisor which results in a
clock frequency that is less than or equal to the target frequency.
For example, if the Base Clock Frequency For SD Clock in the
Capabilities register has the value 33MHz, and the target
frequency is 25MHz, then selecting the divisor value of 01h
yields 16.5MHz, which is the nearest frequency less than or
equal to the target. Similarly, to approach a clock value of
0