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
409
P
ROGRAMMING
M
ODEL
U
SING
SMB
US
P
ROTOCOLS
A transfer is configured by setting data values in the SMBus registers and writing the transfer type to the
smb_start
register. This starts the operation. If the remote device fails to acknowledge when expected to then
the transfer is abandoned with an error. If the interface loses arbitration or detects over-long slave stretching
then the transfer is aborted. The interface will retry an aborted transfer 15 times before abandoning it with an
arbitration error.
Reading from a slave on the serial bus involves these steps:
1
Wait until the busy bit in the
smb_status
register is clear. The interface will ignore accesses while the bit is set.
2
For a Read Byte (but not a Receive Byte) transfer specify the command to be sent by writing to the
smb_cmd
register.
3
Specify the device address and the transfer type by writing to the
smb_start
register. This will cause the
transfer to begin. The busy bit in the
smb_status
register will be set to a one as long as the transfer is in
progress.
4
When the transaction finishes the busy bit will be cleared. This can either be detected by polling the
smb_status
or by enabling the smb_finish interrupt. The error bit indicates that an acknowledgement was not
received from the slave device when the master attempted to start the transaction.
5
Read the data from the
smb_data
register. If one byte was requested, only the lsb field will be valid.
6
If PEC is enabled the
smb_pec
register should be read and checked.
Writing to a slave on the serial bus involves these steps:
1
Wait until the busy bit in the
smb_status
register is clear. The interface will ignore accesses while the bit is set.
2
Specify the command to be sent as the first byte by writing it in the
smb_cmd
register.
3
If data is being sent write it in the
smb_data
register.
4
If PEC is being used the CRC must be calculated by the software and written to the
smb_pec
register.
5
Specify the device address and the transfer type by writing to the
smb_start
register. This will cause the
transfer to begin. The busy bit in the
smb_status
register will be set to a one as long as the transfer is in
progress.
110
6 Bytes
111
Reserved
Reserved encoding. UNPREDICTABLE operation.
Table 288: Read Data Options
(Cont.)
smb_start [10:8]
Data Format
Operation
. . .
S Slave Address Rd
A
1
7
1
1
8
1
Command[15:8] A
1
Command[7:0]
A
A
8
1
Data [15:8]
A
1
Data [7:0]
. . .
8
8
A
P
8
1
1
Xtra [15:8]
A
1
Xtra [7:0]
8
. . .
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