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Light Control
| Re: MCP23x17 question |
Author: Frank van der Hulst
Date: 01-30-10 17:12
> I'm new to the scene. I don't have a whole lot of EE
> background,
Hi,
I'm no EE myself, but have worked with embedded micros, so I have a little knowledge (enough to be dangerous???) about digital electronics and interfacing.
> The /CS line is active high..
For clarity, you should call this signal CS as per the datasheet (/CS implies an active low line).
> If i pull pin 1 low, how do I know how much
> current I'll be sinking and whether or not I'll then be in
> the market for a new motherboard?
Try it and see (but not using a motherboard as the supply!) Hook up a 5V (current-limited if you have one) power supply and a ammeter in series. But probably what the other guy posted is right.
> Section 2.0 "Absolute
> maximum ratings" says "maximum output current sourced by any
> output pin is 25mA" but /CS is not an output, it's an input.
Right. so the 25mA doesn't apply.
> Please help! I've googled for hours and can't find any info
> on controlling this chip via parallel port.. everyone is
> using a PIC and they seem to always tie some pin on the PIC
> right to /CS on the MCP.
Whilst you *could* use printer port pin 1 (strobe) as the CS, you would need to check that the strobe signal timing characteristics match the timings needed by your CS. It would be easier to use one of the data pins on the parallel port as the CS for your chip. You would output a 1 (i.e. 5V) to this bit before starting to clock data out, and hold it high whilst clocking data in/out of the chip, then drop it to 0 when you've finished talking to that chip.
Using this mechanism, you could connect up the SI/SO/SCK bus of 5 of these chips to the same 3 pins of the printer port, and then use one (or more?) the other 5 pins to select which chip(s) you're talking to. So one 8-bit printer port could control 80 outputs.
HTH,
Frank
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| Topics |
Author |
Date |
|
D McLeod |
01-23-10 09:26 |
|
Phil Short |
01-30-10 13:46 |
   |
Re: MCP23x17 question new |
|
Frank van der Hulst |
01-30-10 17:12 |
|
Phil Short |
01-31-10 12:07 |
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