MMCCLK
(CLKRT)
Function clock for
MMC/SD controller
MMC/SD controller
MMC/SD
input clock
card
MMC/SD
Memory clock
on CLK pin
Architecture
1270
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multimedia Card (MMC)/Secure Digital (SD) Card Controller
The memory clock appears on the MMCSD_CLK pin of the MMC/SD controller interface. The memory
clock controls the timing of communication between the MMC/SD controller and the connected memory
card. The memory clock is generated by dividing the function clock in the MMC/SD controller. The divide-
down value is set by CLKRT bits in the MMC memory clock control register (MMCCLK) and is determined
by the following equation:
memory clock frequency = function clock frequency/(2 × (CLKRT + 1))
Figure 26-4. MMC/SD Controller Clocking Diagram
26.2.2 Signal Descriptions
shows the MMC/SD controller pins that each mode uses. The MMC/SD protocol uses the
clock, command (two-way communication between the MMC controller and memory card), and data
(MMCSD_DAT0, MMCSD_DAT0-3, or MMCSD_DAT0-7 for MMC card; MMCSD_DAT0 or
MMCSD_DAT0-3 for SD card) pins.
(1)
I = input to the MMC controller; O = output from the MMC controller.
Table 26-1. MMC/SD Controller Pins Used in Each Mode
Pin
Type
(1)
Function
MMC and SD (1-bit mode)
Communications
MMC and SD (4-bit mode)
Communications
MMC (8-bit mode)
Communication
MMCSD_CLK
O
Clock line
Clock line
Clock line
MMCSD_CMD
I/O
Command line
Command line
Command line
MMCSD_DAT0
I/O
Data line 0
Data line 0
Data line 0
MMCSD_DAT1
I/O
(Not used)
Data line 1
Data line 1
MMCSD_DAT2
I/O
(Not used)
Data line 2
Data line 2
MMCSD_DAT3
I/O
(Not used)
Data line 3
Data line 3
MMCSD_DAT4
I/O
(Not used)
Data line 4
MMCSD_DAT5
I/O
(Not used)
Data line 5
MMCSD_DAT6
I/O
(Not used)
Data line 6
MMCSD_DAT7
I/O
(Not used)
Data line 7