Cec Arbiter; Table 139. Stm32 Cec Arbitration - ST STM32F100 Series Reference Manual

High-definition multimedia interface-consumer electronics control controller (HDMI™-CEC)
24.7.6

CEC arbiter

The STM32F100xx CEC arbiter declines SFT and header arbitration techniques in the
following cases:
•
CEC is a previous initiator retrying a failed transmission and
a)
b)
•
CEC is a new initiator that needs to send a frame and
a)
b)
c)
•
CEC is the last initiator that has to send a frame immediately after its previous frame
and
a)
b)
c)
SFT (ms)
Same initiator retrying
failed transmission
New initiator
Same initiator has to
send another frame
656/709
the leading edge of the start bit is detected before SFT = 9.6 ms. This only occurs
when a new initiator violates the SFT requirement. In this case CEC automatically
synchronizes to the end of the transmitted start bit and participates in the header
arbitration.
CEC initiates frame transmission after 4 nominal bit times (9.6 ms) of the signal
free time condition. CEC automatically switches to follower in case arbitration is
lost (even though no contending device is expected in this case).
the leading edge of the start bit is detected before SFT = 5 minimum bit times
(10.3 ms). This typically occurs when the previous initiator retries a failed
transmission. In this case, CEC automatically switches to reception. Transmission
is retried after the current frame.
the leading edge of the start bit is detected when SFT is between 10.3 ms and
14.4 ms. This is usually caused by a different initiator contending the CEC line.
STM32 CEC automatically synchronizes to the end of the transmitted start bit and
participates in the header arbitration.
CEC initiates frame transmission after 6 nominal bit times (14.4 ms) of the signal
free time condition. It automatically switches to follower in case the arbitration is
lost.
the leading edge of the start bit is detected before SFT = 7 minimum bit times
(14.4 ms). This is caused by a new initiator. CEC automatically switches to
reception and transmission is retried after the current frame, when CEC is no
longer the last initiator.
the leading edge of the start bit is detected when SFT is between 14.4 ms and
19.2 ms. This might be caused by a new late initiator. CEC automatically
synchronizes to the end of the transmitted start bit and participates in the header
arbitration.
CEC initiates frame transmission after 8 nominal bit times (19.2 ms) of the signal
free time condition. CEC automatically switches to follower if the arbitration is lost
(even though no contending device is expected in this case).

Table 139. STM32 CEC arbitration

< 9.6
enter
arbitration
switch to reception
< 10.3 < 14.4
arbitration
switch to reception
RM0041 Rev 6
< 19.2
frame started
enter
frame started
enter
arbitration
≥ 19.2
frame started