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From: "Matt Foster"
Subject: Re: RS232 newbie - in need of assistance!
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
Date: Fri, 3 Jan 2003 22:28:48 -0000
NNTP-Posting-Date: Fri, 03 Jan 2003 22:28:43 GMT
Organization: blueyonder (post doesn't reflect views of blueyonder)
"Matt Foster" wrote in message
> Page 75 rather.
> "Michael F. Coyle" wrote in message
> > "Matt Foster" wrote in message
> > news:bhiR9.2589$KF3.email@example.com...
> > > Ok
> > >
> > > Here's my first attemot at a schematic - please ruthlessly rip it to
> > shreds,
> > > laugh at my incompetence and then give me a better one :-D
> > >
> > > http://matthewfoster.myby.co.uk/lousyattempt.jpg
> > Hi Matt,
> > It's pretty good but I would suggest a few changes:
> > 1. The switches should not be in series with the resistors -- when a
> > is open, the input pin does not go down to zero volts. Instead it
> > around between 0 and 5V because MOS inputs are high impedance.
> > Instead, connect each input to a resistor to 5V and a switch to ground.
> > When the switch is open the resistor pulls the input to 5V; when the
> > is closed, the pin is grounded (and as a side effect, current flows
> > the resistor to ground, which needn't concern us here).
> > A further simplification is to eliminate the resistors altogether!
> > have switches to ground.) Port B on PICs have internal pullup resistors
> > that can be turned on within the program. This saves you the five
> > resistors.
> > 2. If you havent bought the 16F84 yet, consider using the PIC16F628
> > It's a newer part, has more memory, and has a built-in UART which makes
> > programming this application a snap. You would have to do your serial
> > transmission in software on the 84.
> > If you go for the 628, you may have to use a different crystal frequency
> > make the built-in baud rate generator to work correctly. Most standard
> > rates are unrealizable with a 4 MHz oscillator. A better value to use
> > 3.6864 MHz. Then all standard baud rates from 300 to 230,400 are
> > See the 628 data sheet for UART and baud rate generator details.
> > 3. Check your MAX232 data sheet -- mine shows 1uF capacitors, not 10uF.
> > think some older data sheets used 10uF.)
> > 4. I haven't checked your serial port pinouts -- you're on your own
> > But you're definitely on the right track.
> > Hope this helps. Good Luck!
> > - Michael
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