If you have a GT-61 (GT-6144) that you would consider selling or offering in trade, please contact Tom Owad at owad@applefritter.com. Thank you!

Interfacing a SWTP GT-6144 to an Apple I

INTERFACING A SWTP GT-6144 GRAPHICS KIT TO AN APPLE I MICROPROCESSOR

 

The STWP graphics board displays a picture made of a 64 X 96 array of rectangles. The schematic I've enclosed is pretty straigt forward. The .006 MFD capacitor connected between pins 6 and 7 of the 74123 controls the length of time that must elapse between each output of date to the GT-6144. I've been unable to load the date faster than the .005 capacitor will allow.

The rectangles are turned on by sending a horizontal co-ordinate followed by a vertical co-ordinate to the GT-6144. This is clearly explained in the instructions included with the GT-6144. The co-ordinates are stored in location D00A which in basic would be -12278 and would be accomplished by the following: 10 POKE -12278,X where 'X' is hte co-ordinate to be written to the 6144.

The GT-6144 is a kit, and took me about 4 hours to build. The instructions are very good, and my board worked the first time I applied power to it. There is no power supplied with the kit, so you must either build your own, or buy their kit which is sold seperately.

The Gt-6144 is either connected to a TV monitor or to a standard TV thru a video modulator just as you must do with the APPLE 1.

The commands that can be acomplished by the GT-6144 are 1) turn on a rectangle 2) turn off a rectangle 3) display screen as white on black 4) display screen as black on white. The PIA must be set up before you can write to the GT-6144. It must also be set-up after you press the 'RESET' button on your APPLE 1. I get around this problem by making the first statement of my programs an exit in to the subroutine attached to this sheet. This routine not only sets up the PIA but also clears the screen of any rectangles left over from the last program. or the random rectangles that are always present right after powering-up the board.

If you plan to program the graphics in Basic, rember that Basic is very slow, and therefore your graphics will not respond very fast. If you use the POKE command shown above, the following values for X will cause the following actions:

X=0 to 63

send horizontal cordinate and set up to set off rectangle

X=64 to 127

send horiztonal cordinate and set up to set on rectangle

X=128 to 223

send vertical co-ordinate and set on or off rectangle as previously defined in the last horizontal co-ordinate sect

X=240

display screen as black on white

X=241

display screen as white on black

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