C8051F02X Datasheet, PDF (194/272 Pages) Silicon Laboratories – 8K ISP FLASH MCU Family

C8051F020/1/2/3
18.4.5. Status Register
The SMB0STA Status register holds an 8-bit status code indicating the current state of the SMBus0 interface. There
are 28 possible SMBus0 states, each with a corresponding unique status code. The five most significant bits of the
status code vary while the three least-significant bits of a valid status code are fixed at zero when SI = ‘1’. Therefore,
all possible status codes are multiples of eight. This facilitates the use of status codes in software as an index used to
branch to appropriate service routines (allowing 8 bytes of code to service the state or jump to a more extensive ser-
vice routine).
For the purposes of user software, the contents of the SMB0STA register is only defined when the SI flag is logic 1.
Software should never write to the SMB0STA register; doing so will yield indeterminate results. The 28 SMBus0
states, along with their corresponding status codes, are given in Table 1.1.
Figure 18.12. SMB0STA: SMBus0 Status Register
R/W
STA7
Bit7
R/W
STA6
Bit6
R/W
STA5
Bit5
R/W
STA4
Bit4
R/W
STA3
Bit3
R/W
STA2
Bit2
R/W
STA1
Bit1
R/W
STA0
Bit0
Reset Value
00000000
SFR Address:
0xC1
Bits7-3:
STA7-STA3: SMBus0 Status Code.
These bits contain the SMBus0 Status Code. There are 28 possible status codes; each status code cor-
responds to a single SMBus state. A valid status code is present in SMB0STA when the SI flag
(SMB0CN.3) is set to logic 1. The content of SMB0STA is not defined when the SI flag is logic 0.
Writing to the SMB0STA register at any time will yield indeterminate results.
Bits2-0: STA2-STA0: The three least significant bits of SMB0STA are always read as logic 0 when the SI flag
is logic 1.
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Rev. 1.4