C8051T322-GQR Silicon Labs, C8051T322-GQR Datasheet - Page 192

• Manufacturer Part Number: C8051T322-GQR
• Description: 8-bit Microcontrollers - MCU USB-OTP-16K-LQFP32
• Manufacturer: Silicon Labs

Specifications of C8051T322-GQR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

C8051T620/621/320/321/322/323
The SMBCS1–0 bits select the SMBus clock source, which is used only when operating as a master or
when the Free Timeout detection is enabled. When operating as a master, overflows from the selected
source determine the absolute minimum SCL low and high times as defined in Equation 24.1. Note that the
selected clock source may be shared by other peripherals so long as the timer is left running at all times.
For example, Timer 1 overflows may generate the SMBus and UART baud rates simultaneously. Timer
configuration is covered in Section “28. Timers” on page 240.
The selected clock source should be configured to establish the minimum SCL High and Low times as per
Equation 24.1. When the interface is operating as a master (and SCL is not driven or extended by any
other devices on the bus), the typical SMBus bit rate is approximated by Equation 24.2.
Figure 24.4 shows the typical SCL generation described by Equation 24.2. Notice that T
twice as large as T
extended low by slower slave devices, or driven low by contending master devices). The bit rate when
operating as a master will never exceed the limits defined by equation Equation 24.1.
192
Timer Source
Overflows
SCL
LOW
Equation 24.1. Minimum SCL High and Low Times
. The actual SCL output may vary due to other devices on the bus (SCL may be
T
Low
SMBCS1
T
Figure 24.4. Typical SMBus SCL Generation
Table 24.1. SMBus Clock Source Selection
HighMin
0
0
1
1
Equation 24.2. Typical SMBus Bit Rate
BitRate
SMBCS0
=
T
High
T
0
1
0
1
LowMin
=
f
--------------------------------------------- -
ClockSourceOverflow
Rev. 1.1
=
Timer 2 High Byte Overflow
Timer 2 Low Byte Overflow
SMBus Clock Source
--------------------------------------------- -
f
ClockSourceOverflow
Timer 0 Overflow
Timer 1 Overflow
3
1
SCL High Timeout
HIGH
is typically