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Thread: Cables

  1. #1
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    Cables

    Hi there,

    Have an oldie but goodie, HP 4050 printer that only has a Parallel Printer cable input. That is not a problem, but most new computers do not seem to have Parallel Printer ports as everything these days is USB. For my wife and my computers, I fitted a Parallel Printer card with socket attached.

    I know that I can buy USB to Parallel Printer Cable but my question is: if a Parallel Printer plug has 36 pins, and a USB only has about 3/4 contacts, how do the two work?

    Same with VGA to DVI; one has more pins that the other so what are all the pins for?

    Just a passing interest.

    Rex
    What if the Hokey Cokey IS what it's all about?

  2. #2
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    Instead of putting a separate bit on each wire (parallel), they line up all the bits one behind the other (serial).

    Old hard drive ribbon cables were also parallel, SATA cables are serial.

  3. #3
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    Thanks for your reply; not sure I understand. I know that USB is more modern than a parallel printer cable, but if they can get a 36 pin cable to USB, what was the point of 36 pins?

    Rex
    What if the Hokey Cokey IS what it's all about?

  4. #4
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    Back then a lot of stuff was parallel, including the bus on the motherboard. So, I suppose one approach would be to simply extend those wires on out to the printer.

    Wikipedia > Parallel communication
    http://en.wikipedia.org/wiki/Parallel_communication
    In telecommunication and computer science, parallel communication is a method of sending several data signals simultaneously over several parallel channels. It contrasts with serial communication; this distinction is one way of characterizing a communications link.

    The basic difference between a parallel and a serial communication channel is the number of distinct wires or strands at the physical layer used for simultaneous transmission from a device. Parallel communication implies more than one such wire/strand, in addition to a ground connection. An 8-bit parallel channel transmits eight bits (or a byte) simultaneously. A serial channel would transmit those bits one at a time. If both operated at the same clock speed, the parallel channel would be eight times faster. A parallel channel will generally have additional control signals such as a clock, to indicate that the data is valid, and possibly other signals for handshaking and directional control of data transmission.
    ...
    Comparison with serial links

    Before the development of high-speed serial technologies, the choice of parallel links over serial links was driven by these factors:
    • Speed: Superficially, the speed of a parallel data link is equal to the number of bits sent at one time times the bit rate of each individual path; doubling the number of bits sent at once doubles the data rate. In practice, clock skew reduces the speed of every link to the slowest of all of the links.

    • Cable length: Crosstalk creates interference between the parallel lines, and the effect worsens with the length of the communication link. This places an upper limit on the length of a parallel data connection that is usually shorter than a serial connection.

    • Complexity: Parallel data links are easily implemented in hardware, making them a logical choice. Creating a parallel port in a computer system is relatively simple, requiring only a latch to copy data onto a data bus. In contrast, most serial communication must first be converted back into parallel form by a universal asynchronous receiver/transmitter (UART) before they may be directly connected to a data bus.
    The decreasing cost of integrated circuits, combined with greater consumer demand for speed and cable length, has led to parallel communication links becoming deprecated in favor of serial links; for example, IEEE 1284 printer ports vs. USB, Parallel ATA vs. Serial ATA, and SCSI vs. FireWire.

    On the other hand, there has been a resurgence of parallel data links in RF communication. Rather than transmitting one bit at a time (as in Morse code and BPSK), well-known techniques such as PSM, PAM, and Multiple-input multiple-output communication send a few bits in parallel. (Each such group of bits is called a "symbol"). Such techniques can be extended to send an entire byte at once (256-QAM). More recently techniques such as OFDM have been used in Asymmetric Digital Subscriber Line to transmit over 224 bits in parallel, and in DVB-T to transmit over 6048 bits in parallel.
    [...continues...]
    Wikipedia > Parallel port
    http://en.wikipedia.org/wiki/Parallel_port

    Wikipedia > Parallel ATA
    http://en.wikipedia.org/wiki/Parallel_ATA

    Wikipedia > Serial ATA
    http://en.wikipedia.org/wiki/Sata

    Wikipedia > Universal Serial Bus
    http://en.wikipedia.org/wiki/Usb

  5. #5
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    On the DVI to VGA cable, only 4 pins (the ones on the end that look like a cross) are actually used for the digital signal. All the other pins are the old analogue pinouts, and are only there to allow you to use a VGA adapter. In other words, if you plug a DVI cable in, most of the pins are unused.

    With a parallel to USB cable, it is a bit more complicated in that there isn't a direct connection between a pin on the parallel port and a pin on the USB. Instead there is a chip in the cable that is converting the many data pairs of the parallel port into the single pair of the USB port.

  6. #6
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    Quote Originally Posted by SuperSparks View Post
    On the DVI to VGA cable, only 4 pins (the ones on the end that look like a cross) are actually used for the digital signal. All the other pins are the old analogue pinouts, and are only there to allow you to use a VGA adapter. In other words, if you plug a DVI cable in, most of the pins are unused.
    ?

    Wikipedia > DVI (Digital Visual Interface)
    http://en.wikipedia.org/wiki/Digital_Visual_Interface
    DVI 1.0 Specification
    http://www.ddwg.org/lib/dvi_10.pdf

  7. #7
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    Oops, my mistake, I got the pins the wrong way round

  8. #8
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    Could it be due to the time of day over there? What was it, 03:30 | 04:30 AM when you posted that? Had you had any coffee yet? Or, maybe up all night? -what-ever-.

  9. #9
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    You're 12 hours out, it was 3:30 in the afternoon

  10. #10
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    Well, then I don't think you can use that for an excuse.

  11. #11
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    wow, my head is in a spin.

    Thanks SuperSparks, more or less answered my question in a form that I can understand.

    A lot of redundant pins.

    Rex
    What if the Hokey Cokey IS what it's all about?

  12. #12
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    ?

    Looks like to me that out of the 29 pins shown in the diagram above, 23 would be required Digital. The six with "Analog" in the description would probably not be required.

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