C8051F120/1/2/3/4/5/6/7
Rev. 1.2
237
20.
SYSTEM MANAGEMENT BUS / I
2
C BUS (SMBUS0)
The SMBus0 I/O interface is a two-wire, bi-directional serial bus. SMBus0 is compliant with the System Manage-
ment Bus Specification, version 1.1, and compatible with the I
2
C serial bus. Reads and writes to the interface by the
system controller are byte oriented with the SMBus0 interface autonomously controlling the serial transfer of the
data. A method of extending the clock-low duration is available to accommodate devices with different speed capa-
bilities on the same bus.
SMBus0 may operate as a master and/or slave, and may function on a bus with multiple masters. SMBus0 provides
control of SDA (serial data), SCL (serial clock) generation and synchronization, arbitration logic, and START/STOP
control and generation.
Figure 20.2 shows a typical SMBus configuration. The SMBus0 interface will work at any voltage between 3.0 V and
5.0 V and different devices on the bus may operate at different voltage levels. The bi-directional SCL (serial clock)
Figure 20.1. SMBus0 Block Diagram
SFR Bus
Data Path
Control
SFR Bus
Write to
SMB0DAT
SMBUS CONTROL LOGIC
Read
SMB0DAT
SMB0ADR
S
L
V
6
G
C
S
L
V
5
S
L
V
4
S
L
V
3
S
L
V
2
S
L
V
1
S
L
V
0
C
R
O
S
S
B
A
R
Clock Divide
Logic
SYSCLK
SMB0CR
C
R
7
C
R
6
C
R
5
C
R
4
C
R
3
C
R
2
C
R
1
C
R
0
SCL
FILTER
N
SDA
Control
0000000b
7 MSBs
8
A
B
A=B
8
0
1
2
3
4
5
6
7
SMB0DAT
8
SMB0CN
S
T
A
S
I
A
A
F
T
E
T
O
E
E
N
S
M
B
B
U
S
Y
S
T
O
SMB0STA
S
T
A
4
S
T
A
3
S
T
A
2
S
T
A
1
S
T
A
0
SCL
Control
Status Generation
Arbitration
SCL Synchronization
SCL Generation (Master Mode)
IRQ Generation
S
T
A
5
S
T
A
6
S
T
A
7
A
B
A=B
SMBUS
IRQ
Interrupt
Request
Port I/O
1
0
SDA
FILTER
N
7
Summary of Contents for C8051F120
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Page 8: ...C8051F120 1 2 3 4 5 6 7 8 Rev 1 2 26 2 Flash Programming Commands 318 26 3 Debug Support 321 ...
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