CS62180 datasheet(10/50 Pages) CIRRUS

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Common Control Register

The Common Control Register (CCR) deter-

mines global operating characteristics common

to both the transmitter and receiver. It currently

provides for selection of the framing mode

(193S, 193E, SLC-96

® or T1DM), the format of

yellow alarms, the zero suppression format (B7

or B8ZS), loopback operation, and control of

output to RSR.2.

See Figure 4a for an overview of the CCR.

Loopback

CCR.0: LPBK

S e t tin g LP BK (CCR. 0) to "1 " puts the

CS62180B into loopback mode.

While in loopback, the TPOS/TNEG and TCLK

outputs are internally rerouted directly to the

RPOS/RNEG and RCLK inputs, while an un-

framed, all "1’s" stream is output on the

TPOS/TNEG pins. All operating modes, except

blue alarm transmission, remain functional dur-

ing loopback. Note that enabling loopback will

usually invoke an out-of-frame (OOF) error un-

til the receiver can resync to the new framing

alignment. See the section on the Receive Con-

trol Register (RCR) for a description of the

resync options available.

Zero Suppression

CCR.1: B7

CCR.2: B8ZS

B7 and B8ZS select the zero suppression mode.

Setting B7 (CCR.1) to "1" will enable bit 7

zero substitution. This causes any channel word

with all zeros to be transmitted with bit 7 (2

LSB) forced to a "1". B7 mode only affects the

transmitter, the receiver does not decode B7.

Note that bit 7 stuffing can be disabled on an

individual channel basis for clear channel trans-

mission via the Transmit Transparent Registers

TTR1 - TTR3 (see description of transmitter

which follows).

B8ZS coding operates independent of channel

boundaries, and is transparent to all other func-

tions. When using B8ZS, the final transmission

stream is examined before transmission, and

any eight consecutive zeros will be replaced

with a B8ZS code word before transmission.

If B8ZS (CCR.2) is set to a

"1", B8ZS zero substitution will be enabled in

the transmitter. Independent of the setting of

CCR.2, any incoming B8ZS codes will be inter-

cepted by the receiver and replaced with 8

zeros before being processed by the rest of the

receive side. The receiver is always capable of

receving either AMI or B8ZS encoded data.

Note: For T1DM, CCR.1 and CCR.2 should be

set to a "0" since DDS

® equipment assures a 1-

in-8 one’s density.

(MSB)

654321

(LSB)

FM1

FRSR2 EYELMD

YELS

B8ZS

LPBK

See Fig. 4b

0B8ZS

FDL

See Fig. 4b

Bit 2

Disable

0 Transparent 0

Normal

COFA

Bit 2

S-bit

Enable

1 B7 Stuffing 1

Loopback

Figure 4a. Common Control Register (CCR)

CS62180B

DS225PP2

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