General FAQs about parallel printer cables

+S +L Last Update: 14.04.2004 Close

What are "bidirectional" cables?
Printer cables conforming to the "IBM specification" have always been bidirectional. To reduce costs, budget suppliers often omit the signal lines that have up to now been unused during normal printing.

What is Bitronics?
Bitronics (or Bi-Tronics) is a term coined by Hewlett Packard for the so-called "nibble mode" in IEEE 1284. Both terms describe a feedback (from the printer to the PC) through four of the cable´s signal wires, i.e. a four-bit transfer.

So what do EPP and ECP mean?
EPP and ECP are protocols defined in the IEEE 1284 standard for two-directional, 8-bit, high-speed data transfer. EPP was developed by Intel, ECP by Hewlett Packard. There is a third 8-bit mode - the PS/2, or byte mode, which was introduced by IBM, but is rarely used today.
The IEEE 1284 standard therefore defines four modes:

• Compatibility mode (SPP or Standard Parallel Port) mode, also called Centronics mode - 8-bit to the printer, 4-bit in the other direction (nibble mode)
• Byte mode (PS/2 mode) - 8-bit to the printer, 8-bit in the other direction
• EPP (Enhanced Parallel Port) and ECP (Extended Capabilities Port) modes - 8-bit to the printer, 8-bit in the other direction. Both protocols are optimized for speed and are not compatible with each other.

Modern PC hardware supports all four modes, but software support is sometimes limited. For an overview of the IEEE 1284 modes, visit Warp Nine, whose CEO Larry Stein is Chairman of the IEEE 1284 Committee.

So which mode should I use?
EPP and ECP were intended mainly for transferring data to storage media like hard disks, CD drives and streamers. For various reasons, this did not become an established use of these standards. For printing, it does not make much difference, and many PCs are today set to the conventional standard mode because of its reliability.

What are EPP and ECP cables?
Actually, there is no such thing as an EPP or an ECP cable. EPP and ECP are protocols, which are only indirectly related to the cable. What is meant here, are cables that are compliant with the IEEE 1284 standard.

What is an IEEE 1284 compliant cable?
The IEEE1284 standard specifies a cable that meets the minimum requirements for high-speed transmission through parallel ports. The standard was also expected to relieve computer and printer manufacturers' hotlines of many of the inquiries resulting from problems caused by substandard cables.
This standard is the first to specify screening of printer cables as well as the screening methods to be used. In addition, IEEE 1284 specifies a cable with 18 twisted strands with an impedance of 62 ohms. These figures are based on the assumption that manufacturers would also follow all other recommendations of IEEE 1284.
A kind of "quality hallmark" for IEEE 1284 cables, with a multitude of "compliance tests" was also planned, but this was never seriously pursued. Neither, unfortunately, have any general minimum quality requirements been defined (for example for the connectors).

How long can an IEEE 1284 compliant cable be?
A length of 12 meters has been suggested by the developers of IEEE 1284, but this value does not appear in any official publication. However, this applies only if PC and printer conform to the electrical requirements of IEEE 1284 ( Level II Interface)). In practice, the likelihood of this combination is quite low.

1. IEEE 1284 assumes the ideal situation in which both printer and computer conform to the standard ( Level II)), i.e. contain the required driver modules (including 62 ohm output impedance and symmetrical signal edges). As this is not strictly required by the standard, only few devices use these components. In practice, one of the two devices has only a Level I interface, with widely differing conditions, impedance values and asymmetric edges. Here, our WC IBD cable is clearly the better choice. A standard-conformant cable would barely manage the distance of 30 metres that LEUNIG guarantees.
2. Even if both computer and printer truly conformed to IEEE 1284, a LEUNIG cable would still produce better results.
3. A further significant difference is in the screening: IEEE 1284 specifies a screen of copper braiding and foil. This is already a marked improvement compared to the usual cables, but still not sufficient for high-grade cables. That is why LEUNIG's WC IBD and WC PP DN type cables have a dual copper screen of a very different construction.