Shared Configuration
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
6-5
6.4.1 Multi Device Support for the I
2
C Bus
The MSC8144E can share the I
2
C EEPROM device with other MSC8144E devices for loading
the reset configuration word (RCW), as well as for reading configuration during boot loading and
execution. When the bus is shared, the bus must distinguish among reset masters, reset slaves,
and EEPROM slaves:
The reset master (indicated by RCWHR[RM]) holds the STOP_BS signals of all the slaves high
and releases them one by one, thus arbitrating which slave has access to the bus at any moment.
When the master deasserts
STOP_BS
for a slave, the slave device attempts to access an EEPROM
at address 0x57. The actual EEPROM address is 0x50, but the master emulates the EEPROM
using address 0x57 to drive the RCW to each slave in turn.
There are a number of assumptions and limitations imposed when multiple devices share the I
2
C
bus:
1.
For each EEPROM in the system, there must be at least one EEPROM master. The
EEPROM master is also the reset master (RCWHR[RM])
2.
For each EEPROM, there can be 0 or more EEPROM slaves. An EEPROM slave is
defined as a device that reads is RCW from the EEPROM and uses data on the bus
during boot. The number of EEPROM slaves is stored as a single byte at address 0x8F
of the EEPROM.
3.
For each EEPROM, there can be 0 or more reset slaves. A reset slave is defined as a
device that only reads its RCW from the EEPROM but does not read data from it during
boot. The number of reset slaves is stored as a single byte at address 0x11 of the
EEPROM.
4.
Every EEPROM slave must also be a reset slave.
5.
There may be up to 15 reset slaves per EEPROM
6.
As a consequence of the conditions listed in 1–5, the limitations on the number of slaves
is defined as 0
≤
#EEPROM slaves
≤
#reset slaves
≤
15
7.
The lowest numbered reset slave must be a higher numbered slave than the highest
numbered EEPROM slave (for example, if EEPROM slaves are slaves 0–4, then reset
slaves are slaves 5–12).
8.
EEPROM slaves must be numbered sequentially from 0 upward.
9.
All devices connected to the same EEPROM must have
PORESET
asserted
simultaneously, that is, no single device go through the PORESET sequence without the
others.
10.
The EEPROM master must have
HRESET
/
SRESET
asserted unless the slaves are reset as
well
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...