The Norton/PassMark parallel port loopback plug is a passive DB-25 male connector that seats directly on the PC’s parallel port socket and requires no cable or active electronics. It routes five data output lines (pins 2–6, carrying Data Bits 0–4) back to the five status input lines (pins 10–13 and 15), enabling diagnostic software to verify parallel port operation by reading back exactly what was written. The design exploits the IEEE 1284-A signal set, standardised in 1994, which exposes eight data outputs but only five readable status inputs; higher data bits (pins 7–9) cannot be read back without active circuitry and are unused. PassMark Software adopted the identical wiring for their BurnInTest utility, and the plug requires ECP or EPP BIOS mode — the older SPP bidirectional mode is not supported.
25 pin D-SUB male connector
| 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 |
Notes
- The plug is wired as a DB-25 male and connects directly to the female DB-25 socket on IBM-compatible PCs; a straight-through cable may be used if the plug cannot reach the port directly.
- ECP or EPP BIOS mode must be enabled; old SPP (bidirectional) mode is not supported by BurnInTest’s parallel port test.
- The parallel port test is a BurnInTest Professional-only feature; it is not available in the standard edition.
- Compatible with Windows 98 through Windows 11 and Linux via BurnInTest Professional v2.0 and later.
- Pins 7–9 (Data Bits 5–7) and the four control output pins (1, 14, 16, 17) are not connected; the status register provides only five readable input bits, so no passive loopback is possible for the remaining data lines.
- The Norton/PassMark wiring is distinct from the AMI/CheckIt/PC-Doctor variant, which routes the four control outputs (pins 1, 14, 16, 17) to status inputs rather than data outputs.
Signals
- Data Bit 0 (pin 2) — Data output bit 0; wired to Error (pin 15, active-low status input)
- Data Bit 1 (pin 3) — Data output bit 1; wired to Select (pin 13, status input)
- Data Bit 2 (pin 4) — Data output bit 2; wired to Paper Out / PError (pin 12, status input)
- Data Bit 3 (pin 5) — Data output bit 3; wired to Acknowledge (pin 10, active-low status input)
- Data Bit 4 (pin 6) — Data output bit 4; wired to Busy (pin 11, status input)
- Acknowledge (pin 10) — Status input; receives Data Bit 3 from pin 5
- Busy (pin 11) — Status input; receives Data Bit 4 from pin 6
- Paper Out / PError (pin 12) — Status input; receives Data Bit 2 from pin 4
- Select (pin 13) — Status input; receives Data Bit 1 from pin 3
- Error (pin 15) — Active-low status input; receives Data Bit 0 from pin 2
References
- PassMark Hardware — Serial and Parallel Loopback Plugs Technical Specifications
- BurnInTest V9.0 Users Guide — PassMark Software (2018)
- BurnInTest V11 Users Guide — PassMark Software (2024)
- Serial & Parallel Diagnostic Loopback Plugs, Revision 1.01 — David D. Scribner (2002–2003)
- Application Note 062: IEEE 1284 – Updating the PC Parallel Port — National Instruments (1995)