Figure 282. Example Of A Message Transmission With Transmission Error - ST STM32F100 Series Reference Manual

High-definition multimedia interface-consumer electronics control controller (HDMI™-CEC)
Table 141. Software sequence to respect when transmitting a message (continued)
Write Operand1 to TX buffer
Acknowledge byte request by writing 0x00
Poll TBTRF or wait until an interrupt occurs
Write Operand2 to TX buffer
Acknowledge byte request and signal end of
message
Poll TBTRF or wait until an interrupt occurs
Message transmission is completed (TBTRF
and TEOM are set)
Acknowledge successful completion by
writing 0x0
TX_ERROR state
The TX_ERROR state is entered if one of the following error conditions occurs:
•
a directly addressed message block is not acknowledged or a broadcast message
block is negatively acknowledged (acknowledge error)
• the TBTRF bit is not cleared while the requested byte needs to be transmitted (TBTFE
error)
•
an unexpected bit is detected by the bit timing checker/generator (line error)
No error signalling mechanism is specified for the initiator, therefore no specific action is
undertaken apart from aborting the current message and clearing the transmit request flag
TSOM. The error handler decides if retransmission is possible depending on whether
transmission has already failed six times or not. It also sets the transmit request flag if
required.
The controller remains in the TX_ERROR state until the transmit error flag TERR is cleared.
It then waits for an interframe spacing of 2 bit times before of being ready to process the
next message.
An example of a message transmission with errors follows.

Figure 282. Example of a message transmission with transmission error

CEC line
TX buffer
660/709
Software sequences
Start
Header
bit
TSOM=1
Header
RM0041 Rev 6
CEC_CSR R/W
access
-
Write 0x00
Read 0x00
-
Write 0x02
Read 0x00
Read 0x0A
Write 0x0
Opcode Operand1
TERR due
to transmission
TBTRF TBTRF
error
Opcode Operand1
Message abort or retransmission
Status bits
TBTRF TERR TEOM
bit 3 bit 2 bit 1
1 0 0
0 0 0
0 0 0
1 0 0
0 0 1
0 0 0
1 0 1
0 0 0
ai17328b
TSOM
bit 0
0
0
0
0
0
0
0
0