Getting started with Propeller video output...

iam7805

Hi guys,

I'm getting started with using the Propeller chip. Luckily, the Spin language is based on BASIC which is great, because I already know BASIC quite well.

It's confusing me how to output video to a TV though. I read through the manuals and the comments in the TV.spin and Graphics.spin files, and was still confused on how to do this.

So, could anybody give me a straight-forward guide on how to output graphics and text? This Propeller seems very promising for my project, now to learn how to use it.

Thanks,
iam7805

Mike Green

Start with the demo programs that include some kind of tv output (like tv_text_demo). Once you have those working unchanged, you can modify them to suit your purposes. If you have the Demo Board, you have all the hardware you need. If you have a PropStick or just the Propellor chip, you'll need to attach the 3 or 4 resistors needed for the D/A conversion. Look at the Demo Board schematic for the values and how they're connected. The demo programs mostly assume you want to output video rather than a tv broadcast signal. Doing video is simpler since you don't have to change anything.

iam7805

Ok, would this work the way I want (display Hello World on TV)?

' Hello World program 
' Written by iam7805
 
' Required files: 
' hello world.spin (this file) 
' tv_text.spin 
' tv.spin 

VAR 
   byte loop 
OBJ 
   textdisplay : "tv_text" 
PUB start 
   textdisplay.start (12)    ' start display, base pin 12 
PUB message 
   textdisplay.out($48)      ' H 
   textdisplay.out($65)      ' e 
   textdisplay.out($6C)      ' l 
   textdisplay.out($6C)      ' l 
   textdisplay.out($6F)      ' o 
   textdisplay.out($20)      ' <space> 
   textdisplay.out($57)      ' W 
   textdisplay.out($6f)      ' o 
   textdisplay.out($72)      ' r 
   textdisplay.out($6C)      ' l 
   textdisplay.out($64)      ' d 
PUB stop 
   loop := 0 
REPEAT 
   UNTIL loop := 1           ' Spin doesn't have Do...Loop

(The reason i'm asking is because I don't actually have a Propeller yet)

Mike Green

1) PUB and PRI mark the beginning of a subroutine. They're not labels in the way you might expect from Stamp Basic.
2) There are some shortcuts:

CON
SetX = 10
SetY = 11
VAR
long count
OBJ
textdisplay : "tv_text"
PUB Main
textdisplay.start(12)
textdisplay.str(string("Hello World"))
repeat count from 1 to 1000
waitcnt(80_000_000 + cnt) ' waits one second
textdisplay.str(string(SetX,2,SetY,2))
textdisplay.dec(count)

Note that this will put out a video signal, not a broadcast signal (on some tv channel). To do this, you have
to modify the tv_text object. Attached is a modified version of tv_text. Since the pins for the tv D/A have
to be in groups of 4 (as far as the program is concerned), I use the lower 2 bits of the pin number to specify
the tv channel to be used. If the bits are zero, color, progressive scan video is produced. If the bits are 1 through 3, TV channels
2 through 4 are used. For TV, I've disabled color and used interlaced mode for a better display. I recommend
using channel 3. Because of how the RF is produced, there's more static if channels 2 or 4 are used.

Mike Green

Oops ... I forgot about the stripping of indenting in the standard message box. Please correct. Everything except the CON, VAR, OBJ, and PUB should be indented once and the stuff after the repeat statement should be indented twice.