TMXF28155 Supermapper
155/51 Mbits/s SONET/SDH x28/x21 DS1/E1
Data Sheet
June 2002
478
Agere Systems Inc.
20 M13/M23 MUX/DeMUX Block Functional Description
(continued)
FEAC.
In the C-bit parity mode, the third C bit of each DS3 frame, C3, is monitored for FEAC signals. Active FEAC
signals consist of repeating 16-bit code words of the form 0 x5x4x3x2x1x0 0 11111111, where xi can be a 1 or a 0,
and the bits are received right-to-left. The same code word must be received four consecutive times before it is
accepted.
When a code word is accepted, the action taken by the M13 depends on the value of x5x4x3x2x1x0, which may be
an alarm indication, a loopback activation, or a loopback deactivation.
The values of M13_DS1_FEAC_LB_DETx and M13_DS3_FLB_DET bits are not changed if an activate or deacti-
vate control signal is accepted, but the next code word to be accepted is not a channel indication control signal
(010011, 011011, or 100001 through 111100).
Alarm, Status, or Unassigned Signals.
If an FEAC signal is accepted that is not a loopback activate (000111),
deactivate (011100), or channel indication (010011, 011011, or 100001 through 111100) signal, the M13 will set bits
M13_RFEAC_CODE[5:0] = x5x4x3x2x1x0 and M13_RFEAC_ALM_INT to 1; see
Table 229 on page 204
.
Control Signals.
EAC control signals are defined for activating or deactivating a loopback. If a loopback activate
(000111), deactivate (011100), or channel indication (010011, 011011, or 100001 through 111100) is accepted, the
M13 will set bits M13_RFEAC_CODE[5:0] = x5x4x3x2x1x0 (
Table 264 on page 216)
and M13_RFEAC_LB_INT to
1; see
Table 229 on page 204
.
If a loopback activate (000111), followed by the all-DS1 channels indication (010011) is accepted, the device sets
all M13_DS1_FEAC_LB_DETx bits (
Table 263 on page 216
). All M13_DS1_FEAC_LB_DETx bits are cleared if a
loopback deactivate (011100), followed by the all-DS1 channels indication, is accepted.
If a loopback activate (000111), followed by the DS3 indication (011011) is accepted, the device sets the
M13_DS3_FLB_DET bit (
Table 263
). The M13_DS3_FLB_DET bit is cleared if a loopback deactivate (011100),
followed by the DS3 indication, is accepted.
Similarly, if the M13 accepts an activate or deactivate control signal followed by a DS1 channel indication (100001
through 111100), it sets or clears the M13_DS1_FEAC_LB_DETx bit, where x is equal to the binary value of
x5x4x3x2x1x0.
Terminal-to-Terminal Path Maintenance Data Link.
C bits 13, 14, and 15 can be used as a 28.2 kbits/s data link.
These bits are available directly at device output pin RDLDATA (H22). The M13 also contains an internal HDLC
receiver for processing the received data link bits.
HDLC Receiver.
The internal HDLC receiver circuitry is composed of a 128-byte FIFO, a CRC-16 frame check
sequence (FCS) error detector, and control circuits.
The HDLC receiver searches for flag bytes (01111110) and processes the bits received between flag bytes as fol-
lows. The receiver removes zeros that immediately follow any sequence of five consecutive ones. Sequences of
8 bits after zero destuffing are grouped into bytes and written into the FIFO.
As bytes are received, the CRC-16 value, based on the ITU-T polynomial, is calculated. When the closing flag is
received, the receiver checks that the received FCS in the final 2 bytes matches the calculated CRC-16. If
M13_RDL_FCS = 1 (
Table 299 on page 227
) and the FCS does not match, M13_RDL_FCS_ERR (
Table 265 on
page 216
) is set. If M13_RDL_FCS = 0, M13_RDL_FCS_ERR
is held reset at 0. M13_RDL_FCS bit also deter-
mines whether or not the final 2 bytes of the frame are written into the FIFO. They are written into the FIFO only
when M13_RDL_FCS = 0.
The receiver allows frames to be sent back-to-back with the closing flag of one frame shared as the opening flag of
the next frame. If fewer than three complete destuffed bytes are received between flag bytes, the receiver ignores
the data and writes nothing into the FIFO.
FIFO Usage.
The FIFO is large enough to hold one full and two partial standard DS3 LAPD frames of 79 bytes. In
case shorter frames are being transmitted, the M13 can keep track of up to four frames in the FIFO that have not
been read.