Shop OBEX P1 Docs P2 Docs Learn Events
I2C pins — Parallax Forums

I2C pins

NewzedNewzed Posts: 2,503
edited 2006-07-31 14:45 in Propeller 1
Chip, is it OK to use P27 and P28 for I2C instead of P28 and P29?· Running out of space and I can't get to P29.

Thanks

Sid

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2006-07-29 20:39
    Sid, you could probably get away with this if you use P28 as the clock line (as it is with P29). The EEPROM on P28/P29, when it sees clocks on P28, will see a steady high level on P29, so it won't be able to be selected. Likewise with P28/P27.
    Mike
  • NewzedNewzed Posts: 2,503
    edited 2006-07-29 20:49
    Mike, I have SDA ging to P27 and SCL to P28.· Will that fly?

    Sid
  • Mike GreenMike Green Posts: 23,101
    edited 2006-07-29 21:09
    It should work. As long as the clock (SCL) is on P28
  • NewzedNewzed Posts: 2,503
    edited 2006-07-29 21:30
    Thanks, Mike.· Do you know about the VGA connector pins?· Five of the connector pins are grounded but I can only get to one pin.· Will that be OK, or do I have to ground all five?· In case you wonder about all the questions, I'm trying to layout a Propeller board for SuperMill using the LQFP chip and I only have 1.7" of vertical space.· It's really tight.· I don't even know if I will be able to etch it.

    Sid
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2006-07-29 22:11
    Sid,

    Please forgive my intrusion here, but I'm reading something between the lines in your EEPROM question that may have been missed. Interpreting your question literally, Mike's answer is spot on. But if you were wondering whether the Propeller would find the EEPROM at P28/27 on startup and use it to load cog RAM, that won't happen. It needs to be on P28/29 for that.

    I'm guessing this is not what you meant; but it never hurts to be sure, since you're spending all that time to lay out a board...

    -Phil
  • Mike GreenMike Green Posts: 23,101
    edited 2006-07-29 22:25
    Sid,
    From the Wiki, VGA pins 5 and 10 are labelled ground and probably can be considered the same. Pins 6, 7, and 8 are labelled signal returns for red, green, and blue respectively, so you probably have to ground them. I'm sure they're carried separately in the cable to avoid ground loops and the source (the Propeller) is the point where they're all grounded.

    Can you cannibalize a VGA extension cable and bring the leads to the PCB rather than having a connector mounted there?
    Mike
  • NewzedNewzed Posts: 2,503
    edited 2006-07-29 23:00
    Phil, the board is very tight and I can't get to P29.· I have the EEPROM SDA tied to Pin 27 and the EEPROM SCL tied to P28.· Won't that work, or are 28/29 dedicated I2C pins like 0 and 1 on the BS2P?

    Sid
  • NewzedNewzed Posts: 2,503
    edited 2006-07-29 23:04
    Mike, I'll look in my cable collection and see if I have a VGA cable I could sacrifice.· I guess I could always go to Radio Shack and buy one if I have to.

    Sid
  • CJCJ Posts: 470
    edited 2006-07-29 23:06
    The boot sequence only checks on 28/29 for an EEPROM, it is hard coded in the bootup program

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Who says you have to have knowledge to use it?

    I've killed a fly with my bare mind.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2006-07-29 23:14
    Sid,

    Yes, as Mike said, you can put an EEPROM there. Since all pins are general-purpose after startup, it will work fine with your own programs for storing and retrieving data. But EEPROM on P28/27 won't work with the F11 key in the IDE for storing your programs, and it won't work on startup for retrieving your programs to RAM. The Propeller expects EEPROM on P28/29 for those purposes.

    -Phil
  • NewzedNewzed Posts: 2,503
    edited 2006-07-30 15:43
    Mike and Phil, I finally got the board laid out - I think.· The was no room for the eight resistors for the VGA, so I made a separate little board that plugs in with a right angle connector to an 8-pos header at Pins P8-P15.· The board has all the pads necessary to solder·the VGA connector wires, plug a ground pigtail that plugs into the ground bus on the Prop board.· There was enough room on the little VGA board to put a cable clamp to hold the VGA cable secure.· Now all I have to do is to see if I can etch it.

    The EEPROM is tied to P28/29 and the keyboard to P16/17.· I went back to the DB9 programming connector so I wouldn't have to install the FTDI chip.

    Sid
  • Mike GreenMike Green Posts: 23,101
    edited 2006-07-30 16:41
    Hope it goes smoothly. Sounds great!
    Mike
  • Kaos KiddKaos Kidd Posts: 614
    edited 2006-07-31 14:10
    Sid:
    Are you etching or milling the board?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

    Propeller + Hardware - extra bits for the bit bucket =· 1 Coffeeless KaosKidd

    ·
  • NewzedNewzed Posts: 2,503
    edited 2006-07-31 14:45
    KK, I'm going to try to do it with SuperMill.· I'm working on the etch program now so I can do it with my Autorun option.

    Sid
Sign In or Register to comment.