On Sun, Jul 24, 2005 at 10:12:40PM -0700, Daniel Gliebe wrote:
> Ok, I have some news tonight.  I have connected a 74LS04 between the 
> computer's TX pin and the camera's RX pin.  Using HyperTerminal I have 
> successfully sent the Zoom in, Zoom out, and Stop commands to the 
> camera!  I found that the camera expects the data to be exactly 4800bps, 
> 8-bits, 1 stop bit, Even parity, non-inverted (i.e. the line is always 
> high, and high = 0, low = 1).  I couldn't find a MAX232 chip but I 
> thought I'd try this anyway. 

This is unfortunately a good way to tear up your 74LS04. RS232 serial
is specified to swing between -12V and 12V, which is well out of the
input range of the inverter. You probably lucked up and have a port that
swings a lot smaller than that. The conventional technique for limiting
the swing is to use a current limiting resistor and a 4.7V zener diode
at the 74LS04 input. The zener will cap the positive voltage at 4.7V and
the negative voltage to around -0.6V.

> My biggest problem was the fact that a PC can't send non-inverted data, 
> but it can send 4800,8,E,1.

The PC sends RS232 format. It's "inverted" because -12V represents a 1 bit
and 12V represents a 0 bit in RS-232.

>   Where as my BS2 can send inverted data, 
> but it can't send 4800,8,E,1.

The BS2 isn't sending inverted data. It's TTL serial format. Chips like the
MAX232 convert between TTL and RS-232.

>  The 74LS04 allowed me to invert the data 
> coming from the computer's Com port and combination worked.  As far as I 
> can tell, the BS2 can only send 7 data bits with Even Parity and 8 data 
> bits with No parity.  Am I wrong or is that limitation correct?

No clue.

> 
> BTW, here's what this whole project is all about.  A friend gave me a 
> SpeedDome Ultra V dome camera minus the camera block.  I bought two of 
> these Hitachi VK-S274 off ebay for only $150 each.  :-)  I placed one in 
> the dome camera and that works fine.  It also came in handy to help 
> troubleshoot communicating with the second camera.  I want to build my 
> own box for the second camera and program a PIC 16F628 to control 
> various functions of the camera using external buttons.
>  Kinda like a 
> camcorder.  Then I can use it for time lapse protography and various 
> other fun stuff.

PIC USARTS don't calculate parity. However, it will send a 9th bit. So
you can calculate parity and then specify the hardware to send it. 

The PICLIST parity computation page is here:

http://www.piclist.com/techref/microchip/math/bit/parity.htm

> 
> Now here's another question.  At this point I am only familiar with the 
> BS2, PIC 16F84 and 16F628.  I program everything using PicBasicPro.  Do 
> you know if the 16F628 can send 4800,8,E,1 even though the BS2 Can't?  

See above. You'll have to compute the parity yourself. The USART will send it
for you.

> If not perhaps someone could suggest a different PIC that I might find 
> more useful?

I'm not sure beyond your list.

BAJ
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