thanks for your inputs guys

i'm a newbie, and your opinion really matters

my needs are:

- 40 switches
- 40 leds
- 5 displays (3 digits alfanumeric, not LCD)
- 4 AD converters
- UARTS to send and recieve MIDI data

as i understand by your posts, i could divide in and out ports in
groups and control them multiplexing

so, does multiplexing work for both inputs and outputs?

thanks a lot!

Faisal

>I am not really talking about priority encoders in general.  But a note on
>chips of this sort - I do partially agree with you Michael - but it is a
>fact that this is the way it has usually been done in the past.  FOr
>example, how many micro's have you NOT seen that DON'T use 74138's (HC or
>LS),  4028 or 4511 etc. etc., and the like for demuxing a BCD to either
>single or latched outputs, or conversely, chips such as the 74151 etc., for
>line to BCD input multiplexing. Standard muxes and demuxes such as these
>have been used for port expansion on micros this way for many years now, but
>I agree that this imposes limitations, including the need to multiplex your
>inputs/outputs in code if more than 1 line is to be encoded/decoded at a
>time.
>
>Our modern PC's hide all of this inside a BIG PLD, but it is still
>essentially the same thing.
>
>OTOH, there are much better examples available today - in fact one was
>mentioned on the list just recently, the Maxim I2C port expander (MCP23016)
>which communicates with the micro using I2C, and has 3 address lines for
>cascading.  It is fully programmable to assign each of it's 16 lines as
>input or output.
>
>I for one would much prefer to solder a few 14 or 16 pin IC's or even a
>couple of the  28pin Maxim chips as a solution for prototyping than to
>tangle with some micro with 100+ pins with 0.1mm pitch, probably 16bit at
>this size, more complicated in it's architecture, (maybe the PIC18F4720 is
>an exception here), much harder to program and get working, more support
>components, etc, etc, just to get 70 I/O lines, unless the design absolutely
>called for it.
>
>Rgs
>Ian.
>
>-----Original Message-----
>From: pic microcontroller discussion list
>[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Michael Rigby-Jones
>Sent: Wednesday, 12 March 2003 9:45 pm
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: [a bit OT]: suggestions for a huge I/O capabilities
>microcont roller?
>
>
>>  -----Original Message-----
>>  From: Ian McLean [SMTP:ianmclean@OPTUSHOME.COM.AU]
>>  Sent: Wednesday, March 12, 2003 10:27 AM
>>  To:   PICLIST@MITVMA.MIT.EDU
>>  Subject:      Re: [a it OT]: suggestions for a huge I/O capabilities
>>  microcontroller?
>>
>>  Why on earth do you want a micro with over 70 I/O pins ?  You are much
>>  better off using multiplexer chips (many different ones to choose from)
>>  that
>>  can encode 1 to 16 lines (or more) into BCD or even serial/I2C over just
>>  two
>>  wires to the micro,  reducing the port count requirement on your micro
>>  very
>>  dramatically.  This is nearly always how I/O expansion is done on any
>>  micro.
>>  These devices can be cascaded to provide many more than 70 I/O ports if
>>  required.
>>
>>  Building imbedded design solutions of any real significance usually
>>  involves
>>  using more chips than just the micro ;)
>>
>>  Rgs
>>  Ian.
>>
>When you say multiplexer are you talking about a priority encoder? are
>pretty useless for port expansion IMHO,

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