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PerkinElmer Optoelectronics
APPENDIX A Interface Guidelines
A.1 RS-422 Digital Interface
The LC3000 series digital signals are received and transmitted using balanced ,
differential circuits that comply with the data transmission standards set forth in
the EIA RS-422 specification.
All of the differential digital I/O signals on the D-sub 25 connector are labeled
(+) or (-) to indicate polarity. The following definitions apply to each pair of
associated signal lines:
ON: When signal line (+) is more positive than (-).
OFF: When signal line (-) is more positive than (+)
This differential interface is necessary to assure proper camera operation and
optimum high speed data transmission in electrically “noisy” environments often
encountered in industrial applications. RS-422 differential line drivers and
receivers are available from various manufacturers. Examples of suitable drivers
are 75LS192 and 9638 and example of a suitable receiver is 75ALS176B.
Figure 11 shows typical RS-422 input and output circuit configurations with the
type of circuit that should be used to transmit MCLK and LT and to receive
CCLK, LEN and CLT to and from the camera. The following requirements
apply:
1. All of the differential signal output pairs must be terminated at the
receiving end with a 100-120 W resistor line to line.
2. The cable used for each differential signal should be twisted and shielded.
3. The shields should not be used for camera power ground return.
Figure 11 RS-422 Digital I/O Circuit
