MAMEWorld Forums - EmuChat - Re: Parallel port device?

What are you trying to say here, besides worthless conjecture?

> There exist drivers that use a parallel port that work as well as other parallel type devices (e.g. Centronics).

I can’t extract anything from this sentence. I recognise the words, but there's no meaning.

> I'm concerned about parallel ports used a bit later that use a DB-25 connector/cable.

You’re concerned about them? Like you’re worried about their welfare? I guess they might be depressed and suicidal now that they’ve been supplanted by USB.

But that aside, what's special about the DB-25 connector? And what’s a DB-25 cable? The “B” refers to the shell size of a D-subminiature connector, and "25" is the number of pins. It doesn't apply to the cable.

DB-25 connectors were used for many things, including SMPTE 274M digital video, SCSI on Macs and Suns, standard RS-232 serial ports (sometimes with multiple channels on a single port), and different kinds of parallel printer ports.

> From what I know, this was first standardized by IBM.

You need to take a history lesson.

The “standard” parallel port was first used by Centronics in 1970, and was quickly adopted by many computer and printer makers as it was simple to implement and performed better than a serial port for output-only applications.

IBM’s original implementation of the Centronics printer port for the PC enhanced it with bidirectional data lines. However, the feature wasn’t widely used and was subsequently removed. It was re-added on the PS/2 but still wasn’t popular.

The “Bi-tronics” mode that uses status lines to transfer data back to the host a nybble at a time was introduced by HP on the LaserJet 4 and became a de-facto standard. This isn’t a hardware change, it's just a standardised way of (ab)using the control lines for bidirectional data.

The “Enhanced Parallel Port” mode was first used by Zenith, and standardises handshaking for bidirectional data transfer on ports with bidirectional data lines.

IEEE1248 changes the host interface for the port, adding additional DMA transfer modes. It also standardises transfer mode negotiation, RLE compression and daisy-chaining features.

IBM really didn’t have much to do with the development and standardisation of the parallel printer port.