UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 554 o f 792
NXP Semiconductors UM10237
Chapter 21: LPC24XX SD/MMC card interface

5.3.1 Adapter register block

The adapter register block contains all system registers. This block also generates the
signals that clear the static flags in the multimedia card. The clear signals are generated
when 1 is written into the corresponding bit location of the MCIClear register.

5.3.2 Control unit

The control unit contains the power management functions and the clock divider for the
memory card clock.
There are three power phases:
Power-off
Power-up
Power-on
The power management logic controls an external power supply unit, and disables the
card bus output signals during the power-off or power-up phases. The power-up phase is
a transition phase between the power-off and power-on phases, and allows an external
power supply to reach the card bus operating voltage. A device driver is used to ensure
that the PrimeCell MCI remains in the power-up phase until the external power supply
reaches the operating voltage.
The clock management logic generates and controls the MCICLK signal. The MCICLK
output can use either a clock divide or clock bypass mode. The clock output is inactive:
after reset
during the power-off or power-up phases
if the power saving mode is enabled and the card bus is in the IDLE state (eight clock
periods after both the command and data path subunits enter the IDLE phase)

5.3.3 Command path

The command path subunit sends commands to and receives responses from the cards.

5.3.4 Command path state machine

When the command register is written to and the enable bit is set, command transfer
starts. When the command has been sent, the Command Path State Machine (CPSM)
sets the status flags and enters the IDLE state if a response is not required. If a response
is required, it waits for the response (see Figure 21–107). When the response is received,
the received CRC code and the internally generated code are compared, and the
appropriate status flags are set.