PXN20RM Datasheet, PDF (775/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Media Local Bus (MLB)
MLB device that it can transmit data for that logical channel during the next physical channel slot. One
quadlet later, the transmitting MLB device send out a MLB command byte on the signal information line
and the corresponding data on the data line. All other MLB devices (including the controller) have already
compared the logical channel address with their internal table of addresses to determine if they are the
intended recipient of the data on this logical channel.
The receiving MLB device responds with a receive status response on the signal information line one byte
after the transmitting device sends the MLB command byte. Note that synchronous data transmissions
(which is the only data format to support multiple receivers) are not acknowledged, but asynchronous,
control and isochronous data transmissions are acknowledged.
For more information about the Media Local Bus protocol, please refer to the Media Local Bus
Specification.
27.1.4 Modes of Operation
The byte order in which data is transferred between the MLB bus and the MLB device is always Big
Endian; however, a multiplexor at the local channel buffer allows software to select the data byte order of
data within system memory. Big Endian or Little Endian is selected via a software programmable
configuration bit DCCR[MLE].
Table 27-1 illustrates the Big Endian data format. Table 27-2 illustrates the Little Endian data format.
Table 27-1. Big Endian Byte Order
Address
data[31:24]
data[23:16]
data[15:8]
data[7:0]
0x0000_0000
0x0000_0004
0x0000_0008
0x0000_000C
Byte 00
Byte 04
Byte 08
Byte 12
Byte 01
Byte 05
Byte 09
Byte 13
Byte 02
Byte 06
Byte 10
Byte 14
Byte 03
Byte 07
Byte 11
Byte 15
Address
0x0000_0000
0x0000_0004
0x0000_0008
0x0000_000C
Table 27-2. Little Endian Byte Order
data[31:24]
Byte 03
Byte 07
Byte 11
Byte 15
data[23:16]
Byte 02
Byte 06
Byte 10
Byte 14
data[15:8]
Byte 01
Byte 05
Byte 09
Byte 13
data[7:0]
Byte 00
Byte 04
Byte 08
Byte 12
27.2 External Signal Description
The MLB peripheral contains three external pins to interface to the MLB controller. They are shown in
Table 27-3.
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
27-3