View Full Version : Are there restrictions on Propeller pin assignments?
03-25-2009, 10:27 PM
I'm trying to juggle pins around on my PCB design and up till now I've stuck with whatever the default pin assignments were for the various objects for TV, SD card, etc. that I found on the OBEX. Now I'm wondering if there are any inherent restrictions on which pins can be used for what sort of application? For example, is there some fundamental reason why the TV output should begin on pin 12, etc.? and the Prop Plug be on pins 30 and 31, for example. Or is a pin is a pin is a pin is a pin so long as the software and all related objects are adjusted accordingly?
03-25-2009, 10:37 PM
I believe the TV and VGA type objects require pins to start with 0, 8, 16, or 24...·· Look at pages 10&11 "Video Generator" in the datasheet to see why...
The boot EEPROM is on 28,29 and the serial boot loader works off of pins 30,31.
Post Edited (Rayman) : 3/25/2009 3:43:13 PM GMT
03-25-2009, 10:55 PM
In the TV.spin driver, there is a variable _pins (or tv_pins) that is actually assigned from the Graphics_Demo.spin under the DAT section tvparams and passed on to the TV.spin driver.
The _pins variable is setup so that bits 6 to 4 designate the pin group that will be used...
''··· bits 6..4 select pin group:
''····· %000: pins 7..0
''····· %001: pins 15..8
''····· %010: pins 23..16
''····· %011: pins 31..24
''····· %100: pins 39..32
''····· %101: pins 47..40
''····· %110: pins 55..48
''····· %111: pins 63..56
... for the Propeller Demo board, the pin group is set to %001 or pins 8-15.· Of the pin group that you select, ONLY the upper 4-pins are used for TV, the lower 4-pins can be used for whatever you want.· So, again from the Propeller Demo Board, if bits 6-4 of the _pins variable·are set to %001, then the TV will use pins 15,14,13,and 12.· Pins 11,10,9, and 8 are free to use any way you want.
I hope that this makes sense.
Beau Schwabe (mailto:email@example.com)
IC Layout Engineer
Post Edited (Beau Schwabe (Parallax)) : 3/25/2009 4:22:25 PM GMT
03-25-2009, 11:18 PM
Beau and Rayman,
Okay, this is very illuminating information. It will take me a while to make sense of how to shift this around to my application, though. I get nervous when I have to plunge this deep into the underworld of all the software, which I just bet will fork me with assembly code, which I have yet to learn.
You have prevented me from designing myself off a cliff, so thanks to you both for such speedy responses!