User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 14: Serial Configuration Interface Page
407
The Extended protocol mode of the interface supports a much wider range of devices by allowing transactions
other than those specified in SMBus. Up to seven bytes can be written to a device, and up to seven bytes read.
An extended mode transaction consists of a command/address being written to the device followed by either
data being written to the device or a repeated start and data being read from the device.
A write transaction consists of writing a command/address, with the format selected from
, followed
by write data, selected from
. If PEC is enabled then an additional byte from the
smb_pec
register
will be sent before the STOP. (The interface places no interpretation on the bytes, the names command/
address, data and PEC just refer to conventional use of these bytes.)
A read transaction consists of writing the command/address, as shown in
, followed by a repeated
START and reading data, as shown in
. If PEC is enabled then an additional byte will be read into
the
smb_pec
register before the NACK and STOP. The command/address may be null, in which case the
START shown in
will be a standard START not a repeated one.
The extended mode is invoked by setting the extend bit in the
smb_start
register, this changes the
interpretation of some of the other fields. Thus SMBus and extended transactions can be freely mixed.
Table 286: Command/Address Options
smb_start[12:11]
Address Type
Operation
00
Just Read
This is for reads that do not have an address phase. The Start (and slave address)
that is part of the read becomes a regular Start rather than a Repeated Start.
01
Slave
Address
10
Byte
Address
11
16 bit
Address
S Slave Address Wr
1
7
1
1
A
. . .
S Slave Address Wr
Command [7:0]
1
7
1
1
8
1
A
A
. . .
S Slave Address Wr
Command [7:0]
Command [15:8]
1
7
1
1
8
1
8
1
A
A
A
. . .
Table 287: Write Data Options
smb_start [10:8]
Data Format
Operation
000
1 Byte
001
2 Bytes
010
3 Bytes
011
4 Bytes
Data[7:0]
8
1
A
. . .
P
1
Data[7:0]
Data [15:8]
P
8
1
8
1
1
A
A
. . .
Data[7:0]
Data [15:8]
Xtra [7:0]
8
1
8
1
8
1
A
A
A
. . .
1
P
Data[7:0]
Data [15:8]
Xtra [7:0]
8
1
8
1
8
1
A
A
A
. . .
Xtra [15:8]
8
1
A
1
P
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