Hi Rich!

On Mon, 24 Mar 2003, R Wahl wrote:

> I am trying to build a Robot for my Senior Design project.  I am using
> the PIC16F877 MCU, I have it all programmed and ready to go, but I am
> running into Snags while trying to test and Assemble the Robot.  The
> Code works if I am in a Debugging mode, sending predefined signals at
> times, but Now I am running into Interfacing Issues.
>
> I am using the MCU as a Interfacing Chip, it will serve as the
> communication from a Voice Recognition IC to a TTS (Text to Speech IC)
> and a Quadruple Half H Driver (Drives 2 DC Motors using 1 Chip).
>
> My Question is two fold.
>
> First, The output from my Voice Recognition IC is 8 Seperate Bits.  How
> Do I get those 8 seperate bit-lines into one 8-bit Bus (to connect to
> the MCU's PORTB or PORTC, both are 8-bit wide).  Is there a seperate
> Chip that I can but that will pull 8 Bits and set them up to a bus line?
>
> The Second question is jsut the Opposite.  The Quadruple Hafl H Driver
> needs single bit Inputs ( 0/1 settings, which will be converted to
> low/high through an OpAmp).  I was going to use PORTA as an Output port
> to send data to the Half H Driver, and someway able to pull specific
> Bits from the bus to get connected to the H Driver.
>
> If anyone knows How I would go about doing that, Or where I can buy a
> prebuilt Chip that does it for me, I would greatly appreciate it.
>
> Thank you for your Time.
> Rich Wahl

Got your email and the Qs make sense now.

To 'expand' your data from serial to parallel, see HC595.  They can be
cascaded out as far as you need limited only by timing.  But you will need
more than 'just one data pin' to control it.

However, see the piclist archives, search for hc595, and there's a trick
to do it with just one extra pin. Or I think that's how I understand it.

There also 'lesser' shift registers with fewer control options such as
HC164, depending on exactly what other port pins/signals you're allocating
to talk to the target device.

To 'shrink' your data from parallel to serial see HC165.

I also see mentioned a bidirectional PCF8574 but according to Digikey
costs about 2.5x as much per I/O pin. (Meaning that the one chip at $5
replaces the other two totalling about $1.85.)

Have a :) day!

jb

--
jim barchuk
jb@jbarchuk.com

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