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From: "N. Coesel"
Subject: Re: Urgent help needed to blank monitor
Date: Wed, 6 Nov 2002 11:02:20 +0100
Organization: Planet Internet
References: <firstname.lastname@example.org> <2fMx9.160$tQ1.email@example.com>
NNTP-Posting-Date: 6 Nov 2002 10:03:50 GMT
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"Ulrich Peters" wrote in message
> Hello again.
> I think it might be best to expect a certain bit pattern on the parallel
> port, to get one logical high (or low) to control the circuit, because
> the serial port is already in use by a bill acceptor, and the sound card
> is used to provide acustical feedback to the user during the normal
> operation of the software.
> Although a 555 timer could be used to create a delay to switch on the
> monitor, I prefer to use the parallel port solution, because I would
> have control over the shutdown process as well. The equipment has a
> button on its back to power down the equipment. Before my software shuts
> down, the last thing it could do is quickly send a new byte to the
> parallel port, turning off the monitor, before Windows shows its usual
> shutdown dialogs ("saving settings", "closing connections", etc.).
> Unless you send new data to the parallel port, the last byte sent
I wouldn't rely on that. I've made an eprom emulator connected to a parallel
port. Bit banging seemed not to work because the last byte didn't always
'stick' (I didn't lock the printerport). For this reason I made my eprom
emulator mimic a printer port. This is fairly easy. If you have a latch
(like a 74HCT573 or a 74HCT574) and clock it from the strobe line, you can
simply send printer output to your circuit. If you take 2 comparators (like
74HCT688) you can select an on-character and an off-character. The
comparators's outputs should be connected to a flipflop with (pre)set and
clear inputs (like 74HCT74).
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