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C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
17. SMBus
The SMBus I/O interface is a two-wire, bi-directional serial bus. The SMBus is compliant with the System
Management Bus Specification, version 1.1, and compatible with the I2C serial bus. Reads and writes to
the interface by the system controller are byte oriented with the SMBus interface autonomously controlling
the serial transfer of the data. Data can be transferred at up to 1/20th of the system clock as a master or
slave (this can be faster than allowed by the SMBus specification, depending on the system clock used). A
method of extending the clock-low duration is available to accommodate devices with different speed
capabilities on the same bus.
The SMBus interface may operate as a master and/or slave, and may function on a bus with multiple mas-
ters. The SMBus provides control of SDA (serial data), SCL (serial clock) generation and synchronization,
arbitration logic, and START/STOP control and generation. Three SFRs are associated with the SMBus:
SMB0CF configures the SMBus; SMB0CN controls the status of the SMBus; and SMB0DAT is the data
register, used for both transmitting and receiving SMBus data and slave addresses.
SMB0CN
M
T
S
S
A
A
A
S
A
X
T
T
C
R
C
I
S
M
A
O
K
B
K
T
O
R
L
E
D
Q
O
R
E
S
T
SMBUS CONTROL LOGIC
Arbitration
Interrupt
SCL Synchronization
Request
SCL Generation (Master Mode)
SDA Control
IRQ Generation
188
SMB0CF
E
I
B
E
S
S
S
S
N
N
U
X
M
M
M
M
S
H
S
T
B
B
B
B
M
Y
H
T
F
C
C
B
O
O
T
S
S
L
E
E
1
0
D
00
01
10
11
Data Path
Control
Control
SMB0DAT
7
6
5
4
3
2
1
0
Figure 17.1. SMBus Block Diagram
Rev. 1.3
T0 Overflow
T1 Overflow
TMR2H Overflow
TMR2L Overflow
SCL
FILTER
SCL
N
Control
SDA
SDA
FILTER
N
C
R
O
S
Port I/O
S
B
A
R
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