Hi,

there is a ready-made application. It is called at us as Pic-Basic Port
Extender, and it is a pre-programmed PIC16C57, communicating with one pin
serial 2400 Baud. Costs $4 or so.

Regards,
Imre




On Mon, 14 Feb 2000, M. Adam Davis wrote:

> Short Answer: Yes, and not too difficult to accomplish.
>
> Long Answer:
> First you should define your needs, and then your instruction set.  For
> instance, were I to create such a beast, I would probably shoot for 1 PIC, and
> 16 i/o lines.  To make my job easier, I would choose one of the flash chips
> which has an on-board USART, and the ability to program it's own memory
> (16F8xx).
>
> My instructions might be as follows:
> (Pins are number in hex, 0-f, so I only need to specify one digit to refer to
> any pin)
> COx     - Configure Pin x as output
> CIx     - Configure Pin x as input
> CBxyy   - Configure Byte (8 pins, x being 0 or 8) as in/out according to yy
> CCyyyy  - Configure Chip input/output according to yyyy
> CNyyyy  - Configure Notify, notify me (send a read/set response) when one of
>           these pins change states (so I don't have to keep polling you)
>
> SHx     - Set Pin x High
> SLx     - Set Pin x Low
> SWxy    - Set Word (4 pins, x being first pin in the group of four [0,4,8,C])
>           to value y (again, in hex)
> SBxyy   - Set Byte to hex value yy
> SCyyyy  - Set Chip (16 bits) according to yyyy
>
> RBx     - Read bit x
> RWx     - Read word x
> RBx     - Read Byte x
> RC      - Read all bits
>
> Pyyyy   - Reprogram Chip, yyyy being size of program in words
>           This can be used to upgrade the firmware, add new features, etc.
>           This command actually gives control to the bootloader, and is the
>           only command available if the loaded program has a bad checksum.
>
> Chip responses might be:
> Configure Responses:
> C:yyyy:zzzz     - yyyy is the current configuration if I/O
>                   zzzz is the current notify setting
> Read/Set Responses:
> x:b     - b is the current status of pin x (H or L) (so it isn't confused
>           with the next response which is in hex)
> x:y     - y is the current status of word starting at x (y = 0-f)
> x:yy    - yy is the current status of byte starting at x
> C:yyyy  - yyyy is the current status of all i/o (also in response to
>           change in pin state if one of the changed pins is on the Notify
>           list)
> Program response:
> P:yyyy  - Ready to receive yyyy words of program, Checksum first.
>
> One could certianly add new features (A/D, PWM, Timers, etc) as their needs
> warranted.
>
> At any rate, I might actually persue something along these lines.  It would make
> proof-of-concept and prototyping much easier for some projects... One could
> almost think of it as a serial 8255, just more configurable.
>
> There would be more pins available than just 16, which could be used as more
> I/O, A/D, or as an address scheme (every command and response is prefaced by a 1
> digit hex address, four extra pins are used to set that address)
>
> At any rate, that's enough thinking for now.  I will finish my current project
> (rs-232 LCD & keypad interface for home automation) first, then will work on
> this.  Anyone who is interested in the progress of this project should check my
> PIC web site occasionally (http://ubasics.com/adam/pic/)
>
> -Adam
>
> Jonathan Philpott wrote:
> >
> > Hi,
> >
> > I was thinking, would it be possible to have a PIC
> > that could you could "talk" to via a serial port, to
> > give it commands... i was thinking something like
> > this,
> >
> > When you connect to it, it just waits for input, and
> > gives a prompt:
> >
> > >_
> >
> > Then you can give it a command to turn on one of the
> > output lines, a simple one character command would be
> > enough, e.g "o" for on and "f" for off, so:
> >
> > >o1
> >
> > would turn on output line one, and f1 would turn it
> > off.
> >
> > Is this is possible?
> >
> > Jon
> > --
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Talk to your friends online with Yahoo! Messenger.
> > http://im.yahoo.com
>
>