Inter-Integrated Circuit (IIC)
MCF51CN128 Reference Manual, Rev. 6
Freescale Semiconductor
17-13
17.3.8
IIC SMBus Control and Status Register (IICSMB)
NOTE
NOTE
1. A master can assume that the bus is free if it detects that the clock and
data signals are high for greater than THIGH,MAX, however, the SHTF
rises in bus transmission process but bus idle state.
2. When TCKSEL=1 there is no meaning to monitor SHTF since the bus
speed is too high to match the protocol of SMBus.
7
6
5
4
3
2
1
0
R
FACK
ALERTEN
SIICAEN
TCKSEL
SLTF
SHTF
W
Reset
0
0
0
0
0
0
0
0
= Unimplemented or Reserved
Table 17-9. IICSMB Field Descriptions
Field
Description
7
FACK
Fast NACK/ACK enable
— For SMBus Packet Error Checking, CPU should be able to issue an ACK or NACK
according to the result of receiving data byte.
0 ACK or NACK is sent out on the following receiving data byte.
1 Writing an 0 to TXAK after receiving data byte generates an ACK; Writing an 1 to TXAK after receiving data
byte generates a NACK
6
ALERTEN
reserved
SMBus Alert Response Address Enable
— The ALERTEN bit enables or disable SMBus alert response
address.
0 SMBus alert response address matching is disabled
1 SMBus alert response address matching is enabled.
5
SIICAEN
Second IIC Address Enable
— The SIICAEN bit enables or disable SMBus device default address.
0 IIC Address Register 2 matching is disabled.
1 IIC Address Register 2 matching is enabled.
4
TCKSEL
Time Out Counter Clock Select
— This bit selects the clock sources of Time Out Counter
0 Time Out Counter counts at bus/64 frequency
1 Time Out Counter counts at the bus frequency
3
SLTF
SCL Low Timeout Flag
— This read-only bit is set to logic 1 when IICSLT loaded non zero value (LoValue) and
a SCL Low Time Out occurs. This bit is cleared by software, by writting a logic 1 to it
0 No LOW TIME OUT occurs.
1 A LOW TIME OUT occurs.
Note: LOW TIME OUT function is disabled when IIC SCL LOW TIMER OUT register is set to zero.
2
SHTF
SCL High Timeout Flag
— This read-only bit is set to logic 1 when SCL and SDA are held high more than clock
* LoValue/512, which indicates the Bus Free. This bit is cleared automatically.
0 No HIGH TIMEOUT occurs.
1 An HIGH TIMEOUT occurs.