15-2
Intel® PXA255 Processor
Developer’s Manual
MultiMediaCard Controller
The MMC bus connects the card stack to the controller. The software and controller can turn the
MMC clock on and off. The card stack and the controller communicate serially through the
command and data lines and implement a message-based protocol. The messages consist of the
following tokens:
•
Command: a 6-byte command token starts an operation. The command set includes card
initialization, card register reads and writes, data transfers, etc. The MMC controller sends the
command token serially on the MMCMD signal. The format for a command token is shown in
Table 15-1
.
•
Response: a response token is an answer to a command token. Each command has either a
specific response type or no response type. The format for a response token varies according to
the response expected and the card’s mode. Response token formats are detailed
The
MultiMediaCard System Specification Version 2.1
.
•
Data: data is transferred serially between the controller and the card in 8-bit blocks at rates up
to 20 Mbps. The format for the data token depends on the card’s mode.
Table 15-2
shows the
data token format for MMC mode and
Table 15-3
shows the data token format for SPI mode.
In MMC mode, all operations contain command tokens and most commands have an associated
response token. Read and write commands also have a data token. Command and response tokens
are sent and received on the bidirectional MMCMD signal and data tokens are sent and received on
Table 15-1. Command Token Format
Bit Position
Width (bits)
Value
Description
47
1
0
start bit
46
1
1
transmission bit
[45:40]
6
x
command index
[39:8]
32
x
argument
[7:1]
7
x
CRC7
0
1
1
end bit
Table 15-2. MMC Data Token Format
Stream Data
Block Data
Description
1
0
start bit
x
x
data
no CRC
x
CRC7
1
1
end bit
Table 15-3. SPI Data Token Format
Value
Description
11111110
start byte
x
data
x
CRC16
Summary of Contents for PXA255
Page 1: ...Intel PXA255 Processor Developer s Manual January 2004 Order Number 278693 002 ...
Page 24: ...xxiv Intel PXA255 Processor Developer s Manual Contents ...
Page 30: ...1 6 Intel PXA255 Processor Developer s Manual Introduction ...
Page 310: ...7 46 Intel PXA255 Processor Developer s Manual LCD Controller ...
Page 330: ...8 20 Intel PXA255 Processor Developer s Manual Synchronous Serial Port Controller ...
Page 358: ...9 28 Intel PXA255 Processor Developer s Manual I2 C Bus Interface Unit ...
Page 488: ...13 36 Intel PXA255 Processor Developer s Manual AC 97 Controller Unit ...
Page 572: ...16 30 Intel PXA255 Processor Developer s Manual Network SSP Serial Port ...
Page 599: ...Intel PXA255 Processor Developer s Manual 17 27 Hardware UART ...
Page 600: ......