CheckIt Loopback
| Name | Pin | Pin | Name |
|---|---|---|---|
| Busy | 11 | 17 | Select Input |
| Acknowledge | 10 | 16 | Initialize |
| Paper end | 12 | 14 | Auto Feed |
| Select | 13 | 1 | Strobe |
| Data Bit 0 | 2 | 15 | Error |
Norton/Passmark LoopBack
| Name | Pin | Pin | Name |
|---|---|---|---|
| Data Bit 0 | 2 | 15 | Error |
| Data Bit 1 | 3 | 13 | Select |
| Data Bit 2 | 4 | 12 | Paper Out |
| Data Bit 3 | 5 | 10 | Acknowledge |
| Data Bit 4 | 6 | 11 | Busy |
Loopback, or loop-back, refers to the routing of electronic signals, digital data streams, or flows of items back to their source without intentional processing or modification. This is primarily a means of testing the transmission or transportation infrastructure. A communications transceiver can use loopback for testing its functionality. For example, a device transmit pin connected to its receive pin will result in the device receiving exactly what it transmits. Moving this looping connection to the remote end of a cable adds the cable to this test.

