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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hi All,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>On my daily adventures with
microcontrollers I am faced with another I/O problem. Please forgive me my silly
questions since I’m not an electronics expert. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>Here goes:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>I have a MCU with 2 8-bit
ports <span class=GramE>available,</span> one of them is the A/D. Since I’m
connecting an LCD to the MCU as well, I need one port as the LCD’s data
bus. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>So that leaves me without any
pins to light my LED matrix (32 <span class=SpellE>leds</span> = 4x8) and scan
my key matrix (up to 32 keys). <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>I thought about putting an
SN74CBT16233 on the 2 8-bit ports, this will give me another 16 I/O lines. This
IC is a 16-bit 1-of-2 FET multiplexer. So I would <o:p></o:p></span></font></p>
<p class=MsoNormal><span class=GramE><font size=2 face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>put</span></font></span><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial;
mso-ansi-language:EN-GB'> the A/D and LCD data bus on one output of the
multiplexer and the key matrix + led matrix on the other output of the
multiplexer. The key and led matrix <o:p></o:p></span></font></p>
<p class=MsoNormal><span class=GramE><font size=2 face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>would</span></font></span><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial;
mso-ansi-language:EN-GB'> be 8 rows which I want to put power on sequentially,
and then use 4 columns to light the <span class=SpellE>LEDs</span> and 4
columns to scan the keys. Does this <span class=GramE>make</span> <o:p></o:p></span></font></p>
<p class=MsoNormal><span class=GramE><font size=2 face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>any</span></font></span><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial;
mso-ansi-language:EN-GB'> sense? I’m just trying to find a way to hook up
all this <span class=GramE>I/O</span>. <span class=SpellE>Argh</span>! <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>It’s ok if I lose some
brightness by multiplexing, as long as they have a decent visibility I’m
happy. I’m also concerned that the MCU might go to heaven if I <o:p></o:p></span></font></p>
<p class=MsoNormal><span class=GramE><font size=2 face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>make</span></font></span><font
size=2 face=Arial><span lang=EN-GB style='font-size:10.0pt;font-family:Arial;
mso-ansi-language:EN-GB'> it source and sink the current for the <span
class=SpellE>LEDs</span> (even when only one LED gets lit at a time for a very
short period). <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>Thanks for any suggestions…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'>Bert (very tired and going to
bed now)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB'><o:p> </o:p></span></font></p>
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