Inter-Integrated Circuit Peripherals
UG0331 User Guide Revision 15.0
560
15.4.6
Frequency Register
The Frequency register is required to calculate the real-time timeout logic. The following table describes
the Frequency register.
5
SMBSUS_NI status
R
0bX
Status of SMBSUS_NI signal. SMBUS_NI is a Suspend mode
signal from fabric to MSS. It is used if the core is slave/device.
Upon resuming, the SMBSUS_NI returns High. The system
then returns all devices to their operational state.
SMBSUS_NO and SMBSUS_NI are separate signals (not
wired-AND). If the I
2
C is part of a host-controller, SMBSUS_NO
can be used as an output; if I
2
C is a slave to a host-controller
that is implemented SMBSUS_N, then only SMBSUS_NI's
status is relevant.
4
SMBALERT_NO control
R/W 0b1
SMBALERT_NO control; SMBALERT_NO is a wired-and-
interrupt signal from the MSS to fabric.
It is used in Slave/Device mode if the core wants to force
communication with a host.
3
SMBALERT_NI status
R
0bX
Status of SMBALERT_NI signal. SMBALERT_NI is a wired-
and-interrupt signal from the MSS to fabric.
It is used in Master/Host mode, if the slave/devices want to
force communication with a host.
2
SMBus enable
R/W 0
0: SMBus timeouts and status logic disabled (standard I
2
C bus
operation)
1: SMBus timeouts and status logic enabled
1
SMBSUS interrupt enable
R/W 0
0: SMBSUS interrupt signal (SMBS) disabled
1: SMBSUS interrupt signal (SMBS) enabled
0
SMBALERT interrupt enable R/W 0
0: SMBALERT interrupt signal (SMBA) disabled
1: SMBALERT interrupt signal (SMBA) enabled
Table 532 •
Frequency Register (FREQ)
Bit
Number Name
R/W
Reset Value Description
7:0
Frequency R/W
0x08
PCLKx frequency in MHz from 1 to 255.
If the PCLKx frequency is used, and SMBus is enabled, the SMBus
timeouts are configured per the SMBus specification. If another timeout
value is desired, scale the frequency value as per the following formula:
Timeout scale = Fscale/Factual
If the actual PCLKx frequency is 100 MHz, and a scale down is desired
that results in a 3 ms timeout rather than 25 ms timeout, then:
Fscale = 3/25 x Factual = 0.12 x 100 = 12 MHz
Writing 12 into the Frequency register has the effect of reducing
maximum timeout count value and reducing the real-time timeout from
25 ms to 3 ms.
Table 531 •
SMBus Register (SMBUS)
(continued)
Bit
Number Name
R/W
Reset
Value Description