From: "Michael F. Coyle"
Subject: Re: RS232 newbie - in need of assistance!
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sat, 04 Jan 2003 00:21:43 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 19:21:43 EST
Organization: Optimum Online
"Matt Foster" wrote in message
1. I wouldn't recommend 5.0688 MHz clock frequency. See my reply elsewhere
2. On the 628, the UART transmit is on pin 8 (overrides RB2); receive is on
pin 7 (overrides RB1). If you use the built-in UART you will have to move
the inputs on those lines elsewhere. Perhaps use RB3-7 (pins 9-13).
3. Some posters have suggested not connecting the receiver since you are
just sending data to the PC, not the other way around. I would suggest
keeping it connected; after all, we're only talking two wires here. And it
makes the design a little bit more versitile in case you want to keep
playing with it after your assignment's done. The hardware is already
there, why not use it?
4. My contribution to The Great Resistor Controversy. The other poster had
a point about the possibility of an input pin inadvertantly becoming an
output and possibly shorting out when the button is pressed. Taking that
into consideration, here's what I'd do: enable the PIC Port B weak pullups,
and on the pin, connect each switch to ground through a 1K resistor. Worst
case sceanario: if the input accidently becomes an output and that output
wants to be high and the switch is closed, the port sources only 5 mA -- no
sweat. As an input, if the switch is open, the internal pullup pulls the
pin high. If the switch is closed, then a resistive divider is formed with
the internal pullup (about 25K and the external 1K. The voltage on the
input pin is about 0.2 V, a nice good "0".
5. You're getting lots of good advice from the group -- some of it
contradictory. Hang in there.