On Mon, Feb 21, 2011 at 12:06 PM, Lee Privett <[email protected]> wrote:
> Dave, it my help those like me with less knowledge of such things to know > exactly what QL'ers could make use of a back plane for, plugging in > additional peripherals such as floppy drive adapter are already realised > with through connections on the memory unit. > A backplane allows you to place each card in its own slot. It multiplies the QL's expansion port into three, four or more ports. This means cards don't need to use through-connectors. It also allows them to be powered by an external power supply, if you have so many cards that they strain the QL power supply. This is especially helpful if you have a Gold Card, SGC or Aurora... Imagine a Gold Card in a slot, a QubIDE in one slot, and still having a slot free. Backplanes are usually used if you remove your QL circuit board from the original case and put it in a regular PC case. There are different formats of backplane that allow you to place your QL in a different case - usually an older AT computer case with an AT power supply. AT power supplies have a ON/OFF switch to operate the PSU directly. ATX power supplies are more complicated. They are switched on an off electronically by a control signal from the computer's circuit board - circuitry QLs and most pre-1995 computers do not have. The switch is connected to the computer, and is a momentary switch. It tells the computer that a power toggle was requested, and the computer PCCB can refer to its internal settings to decide what to do. This allows the computer to shut itself down, and to define whether the computer should stay off or turn on after a power failure. There are no QL backplanes which work with ATX power supplies, because they lack that power control circuitry. There is a good description of ATX power and control here: http://pinouts.ru/Power/atx_v2_pinout.shtml Taking power from pin 9 (5VSB) we can operate a bistable flip-flop which is operated by a momentary switch, and feeds the flip-flop's output to pin 16 (/PS_ON). In plain English, a bistable flip-flip is a circuit that, when triggered, changes state then stays in that state until triggered again. So each time you press the switch, the output changes from 1 to 0 or from 0 to 1. Feeding this back to the control circuit of the power supply allows the power supply to turn on and off all the other power outputs as required. The circuit to control this is so trivial, it should really be used in all new designs where a PSU may be needed. Dave _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
