CS62180 datasheet(29/50 Pages) CIRRUS

29 / 50 page

Each of the eight bits of the RSR (Figure 21)

corresponds to an alarm condition. A bit in the

RSR is set when the corresponding alarm is de-

tected. It will be cleared by a direct read (a burst

read will have no effect) of the RSR, unless the

alarm condition persists (see Alarm Servicing,

below). TCLK is used to clock the internal cir-

cuitry which clears RSR after it is directly read;

therefore, a 1.544 MHz signal must always be

input to TCLK, even for a "receiver-only" appli-

cation. The status pins which correspond to

many of the RSR bits operate in real time. They

go high when the error is detected, and return

low either immediately, or as soon as the error

condition is cleared. Alarms are reported syn-

chronously with the emergence of the offending

bits on RSER. See Figure 22, and the corre-

sponding alarm description below for further

description of status pin timing.

Receive Loss of Sync

RSR.0: RLOS

RLOS (RSR.0) goes high when a receiver resync

is in progress. When the receiver is set to auto

resync (RCR.1 = 0), the receiver will commence

resync when an OOF event or loss of carrier is

detected. If in response to an OOF, RLOS transi-

tions high synchronously with the output of the

offending F-bit on RSER (see RCR.6).

If in response to an RCL, RLOS goes high

with the 128th

±1 consecutive zero bit.

The RLOS pin will return low one bit period

prior to the F-bit of the second frame after the

new alignment has been declared (timing signals

will reset at the start of the new superframe). Re-

fer to Receiver Synchronization, above, for more

information.

Receive Blue Alarm

RSR.1: RBL

RBL (RSR.1) will transition high when a blue

alarm is detected, and is updated at the begin-

ning of odd-numbered frames.

A blue alarm is reported whenever

unframed all ones occurs, as per Bellcore

TR-TSY-000191. The algorithm used is to simul-

taneously check for an out-of-frame (OOF)

condition, and check for 14 or less zeros out of

13,895 bits. All bits, including frame bits, are

tested. RBL goes high on a frame boundary.

RBL goes low immediately (indicating the termi-

nation of the AIS condition) if OOF goes low, or

if 15 or more zeros are counted and the number

of bit periods is less than or equal to 13,895.

RBL is reported on pin 3 of the 44-pin PLCC

package. There is no status pin corresponding to

RBL on the 40-pin DIP package.

B8ZS/COFA Detect

RSR.2: B8ZSD

B8ZSD (RSR.2) is a multifunction bit. It can be

configured either to report the detection of B8ZS

codes, or to indicate a change of framing align-

ment. This selection is performed through the

setting of CCR.6 (see Common Control Register,

above). There is no status pin corresponding to

RSR.2.

If CCR.6 is clear, RSR.2 will go high every time

a B8ZS code is detected in the incoming T1

data. This detector remains operational, whether

or not B8ZS substitution has been enabled via

CCR.2.

CS62180B

DS225PP2

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