
bit transmitted on the channel. To initiate transmission of a message byte in the 
FEAC channel, write the desired byte in the form 
“
mmmxxx
”
 into bits 15
–
10 of 
the TXFEAC_ERRPAT register. A 1 must be written to Enable FEAC 
Transmission [bit 9]. Transmission of the flag (11111111) and the 0s on either 
side of the 
“
xxxmmm
”
 pattern is automatic. Ten repetitions of the message are 
sent before an interrupt is issued on the DL_INT pin. The interrupt also appears 
in the RXFEAC_VER register to request a new byte from the processor. To clear 
the interrupt, you must write the TXFEAC_ERRPAT register. Each time a new 
byte is written, 10 transmissions of that byte (and flag) will automatically occur. 
Interrupts from the transmit FEAC channel will occur at a rate of approximately 
one interrupt per 17 ms.
If you write a 0 to Enable FEAC Transmission [bit 9], then continuous 
transmission of idle flags is enabled and no interrupts are issued until a byte of the 
proper format is written to the TXFEAC_ERRPAT register. Interrupts from the 
FEAC channel transmitter appear on Transmit FEAC Interrupt [bit 8] in the 
RXFEAC_VER register [0x3C].
2.0 Functional Description
CN8223
2.8 FEAC Channel and HDLC Data Link Programming
ATM Transmitter/Receiver with UTOPIA Interface
2-44
Conexant
100046D
2.8  FEAC Channel and HDLC Data Link 
Programming
This section discusses the use and programming requirements for the FEAC 
channel and HDLC data link. The FEAC channel is used in DS3 mode; the 
HDLC data link is used by DS3, E3, and STS-1/3 framers.
2.8.1  FEAC Channel Transmitter
The FEAC Channel transmitter is under control of the PHY Type [bits 2
–
0], 
External Framer [bit 5] of CONFIG_1 [0x00], Transmit Alarm Control [bits 9
–
4 
of CONFIG_2 [0x01], Enable FEAC Transmission [bit 9], and Transmit FEAC 
Data [bits 15
–
10] of TXFEAC_ERRPAT [0x03]. An interrupt for use with FEAC 
channel operations is available on the DL_INT output pin, and status bits for 
determining the interrupt source are located in the RXFEAC_VER register 
[0x3C].
The PHY type must be set to internal DS3 for FEAC channel transmission to 
take place. In DS3 mode, the last C bit in subframe 1 of the M-frame is used for 
transmission. Setting the Transmit Alarm Control [bits 9
–
4] for transmission of 
AIS disables transmission of the FEAC channel. Transmission of yellow alarm or 
idle code has no effect on FEAC channel transmission.
The TXFEAC_ERRPAT register controls the byte to be transmitted on the 
FEAC channel. All messages for transmission on the FEAC channel must be in 
the form 
“
0xxxmmm011111111
”
. The right-most bit of this sequence is the first