Patton electronic 2701/C Switch SW2-2 CRC-4 Multiframe, SW2-2 Option, Switch SW2-3 Data Inversion

Every other pulse is inverted from the previous pulse in polarity, so that the signal can be effectively transmitted. This means, however, that a long sequence of zeros in the data stream will cause problems, since the NTU receiving the signal relies on the signal to recover the 2.048 Mb/s clock.

If you must use AMI, you should ensure that the data terminal equipment connected to the unit provides a minimally accept- able pulse density. For this reason, there are advantages to using HDB3 instead. AMI coding does not inherently account for ones density. To meet this requirement, the user should ensure that the data inherently meets pulse density requirements.

Switch SW2-2: CRC-4 Multiframe

In framed mode, SW2-2 is used for CRC-4 MF. When CRC-4 is enabled, the unit monitors the incoming data stream for CRC-4 errors. It transmits CRC-4 error counts to the transmitting unit. When using timeslot zero (TS0), excessive errors may cause loss of frame or loss of sync. If CRC- 4 MF is used, both units must be set for set for CRC-4 MF. Otherwise, the one using CRC-4 MF will detect loss of sync.

SW2-2	Option
Off	CRC-4 Disabled
On	CRC-4 Enabled

Note When the data rate is set to 2.048Mb/s, then the unit is forced into G.703 mode, and it transmits user data on all 32 time-lots. There is no framing information; therefore, the CRC4 MF (SW2-

2)switch is ignored. In all other rate settings, the unit employs G.704 framing; TS0 is reserved for signaling.

Switch SW2-3 Data Inversion

Set Switch S2-3 to determine whether or not the data stream from the local DTE is inverted within the Model 2701 before being passed to the G.703/G.704 network. An inverted data stream may be required when you use the Model 2701 to communicate with a G.703 device (that inverts the data) on the remote end. In typical installations, data inversion is not necessary.

SW2-3	Option
Off	Data not inverted
On	Data inverted

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