Sft Option Bit; Figure 295. Sft Of Three Nominal Bit Periods - STMicroelectronics STM32F05 series Reference Manual

RM0091
The Figure 295

Figure 295. SFT of three nominal bit periods

A configurable time window is counted before starting the transmission.
In the SFT=0x0 configuration the HDMI-CEC device performs automatic SFT calculation
ensuring compliancy to the HDMI-CEC Standard:
●
2.5 data bit periods if the CEC is the last bus initiator with unsuccessfull transmission
●
4 data bit periods if the CEC is the new bus initiator
●
6 data bit periods if the CEC is the last bus initiator with successfull transmission
This is done to guarantee the maximum priority to a failed transmission and the lowest one
to the last initiator that completed successfully its transmission.
Otherwise there is the possibility to configure the SFTbits to count a fixed timing value.
Possible values are 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5 data bit periods.
28.4.1

SFT option bit

In case of SFTOPT=0 configuration SFT starts being counted when the start-of-
transmission command is set by software (TXSOM=1).
In case of SFTOPT=1, SFT starts automatically being counted by the HDMI-CEC device
when a bus-idle or line error condition is detected. If the SFT timer is completed at the time
TXSOM command is set then transmission starts immediately without latency. If the SFT
timer is still running instead, the system waits until the timer elapses before transmission
can start.
shows an example for a SFT of three nominal bit periods
last bit of previous frame
Doc ID 018940 Rev 1
HDMI-CEC controller (HDMI-CEC)
Start bit
703/742