50 pin M/50 male connector at the computer.
50 pin M/50 female connector at the cable.
The Dataproducts M/50 (also called the Winchester connector) is the printer-side variant of the Dataproducts parallel interface, a de facto industry standard developed independently of Centronics and used on Dataproducts line printers from the 1970s onwards. It carries an 8-bit unidirectional data bus at TTL levels together with handshaking via a high-true Data Strobe from the host and a high-true Demand signal from the printer, distinguishing it fundamentally from the Centronics interface which uses active-low signalling on a 36-pin micro-ribbon connector. The M/50 block connector carries the same 50-pin signal assignment as the DD-50 D-sub variant; the host side uses a standard 37-pin D-sub (DC-37). DEC adopted the Dataproducts-compatible interface for its LP-series line printers (LP25, LP26, LP27, LP29, LP32, LP37) connecting via the BC27A cable, and the LP11/LPV11 controllers implement this interface for UNIBUS-based PDP-11 systems.
| Pin | Return | Dir | Description | Active State |
|---|---|---|---|---|
| CC | EE | IN | Ready | High |
| Y | AA | IN | On Line | High |
| E | C | IN | Demand | High |
| j | m | OUT | Data Strobe | High |
| B | D | OUT | Data 1 | n/a |
| F | J | OUT | Data 2 | n/a |
| L | N | OUT | Data 3 | n/a |
| R | T | OUT | Data 4 | n/a |
| V | X | OUT | Data 5 | n/a |
| Z | b | OUT | Data 6 | n/a |
| n | k | OUT | Data 7 | n/a |
| u | w | OUT | Data 8 | n/a |
| z | BB | OUT | Parity | n/a |
| d | f | IN | Ident 0 | n/a |
| a | c | IN | Ident 1 | n/a |
| v | x | OUT | Interface Verify | Low |
| HH | K | OUT | +5 VDC (Test) | High |
| r | t | IN | Parity Error | High |
| M | P | IN | Bottom of Form | High |
| S | U | IN | Top of Form | High |
| p | s | OUT | Paper Instruction | High |
| A | H | OUT | Buffer Clear | High |
| W | Y | IN | Paper Moving | High |
| FF | DD | IN | Paper Moving | High |
| e | h | IN | Not VFU | High |
Notes
- Direction is Host (Computer) relative Peripheral (Printer).
- Return is Ground signal for Unbalanced and the Negative Signal for Balanced.
- The M/50 block connector (Winchester) carries the same 50-pin signal assignment as the DD-50 D-sub shell used on other Dataproducts printer models; the two shells are not mechanically interchangeable despite sharing the signal map.
- The short-line variant uses single-ended (unbalanced) TTL signalling with a maximum recommended cable length of approximately 40 feet (12 m). A long-line adapter enables differential (balanced) operation, extending the cable run substantially; in the balanced mode the Return line carries the negative signal rather than ground.
- Data Strobe polarity may be configured on some printers for leading, middle (default), or trailing-edge sensing.
- Transfer rates of up to 300,000 characters per second are supported by compatible Dataproducts-interface printers.
Signals
- Ready — high-true output from printer indicating AC and DC power are present, paper is loaded, and no check condition exists.
- On Line — high-true output from printer; asserted when Ready is true and the operator has activated the ONLINE switch.
- Demand — high-true output from printer (also called Data Request) synchronising host data transmission with printer timing; the host may send the next character only when Demand is asserted.
- Data Strobe — high-true pulse from host to printer latching the parallel data lines into the printer; polarity and active edge are configurable on some printers.
- Data 1–Data 8 — 8-bit parallel data word from host to printer at TTL levels; all eight lines are presented simultaneously and latched on the active edge of Data Strobe.
- Parity — parity bit accompanying the 8-bit data word; direction host to printer.
- Ident 0, Ident 1 — printer-to-host identification signals; function varies by printer model.
- Interface Verify — active-low loopback signal used to verify interface continuity between host and printer.
- +5 VDC (Test) — +5 V test point supplied by the host for interface verification purposes.
- Parity Error — high-true signal from printer to host indicating a parity mismatch on received data.
- Bottom of Form — high-true signal from printer indicating the paper is at the bottom-of-form position (also referred to as IBOF on some variants).
- Top of Form — high-true signal from printer indicating the paper is at the top-of-form position.
- Paper Instruction — host-to-printer line carrying the Dataproducts Vertical Format Unit (DVFU) signal; timing and polarity match the data lines and it is latched by Data Strobe.
- Buffer Clear — high-true signal from host instructing the printer to clear its input buffer.
- Paper Moving — high-true signal from printer indicating paper motion is in progress; listed twice in the pin table corresponding to two separate pins (W/FF) whose individual functions are not further distinguished in available documentation.
- Not VFU — signal from printer; precise function not publicly documented.
References
- Printronix P6000L/P6200L Line Printers User’s Reference Manual — Chapter 7: Interfaces
- DEC Cables Reference Guide (BC27A cable, LP-series printers)
- LP11/LS11/LA11 Line Printer User’s Manual (EK-LP11S-OP-001)
- Dataproducts line printer technical manuals (Models 2230, 2420, 2440, 2470) — Computer History Museum catalogue 102753073