Hi Brian,

I am not familiar with the HandyBoard expansion board.
Because the HandyBoard has dedicated input and output ports (not bidirectional),
two ports are required for each signal on the I2C bus.

I used the existing input ports but added a 74HC574 latched octal D-type
flip-flop to the Y0 address line on the HandyBoard to provide an output. The Y0
selects for a read address of 0x4000 in the HandyBoard memory map. I chose
0x4FFF because, well, I don't remember.

So, each of the SDA and SCL lines have a separate in and out line.
The device I was communicating with has circuitry to connect this to a
bidirectional bus. Also, the lines are inverted logic as I had probably run out
of inverters on the target board. This was a long time ago and I no longer use
the HandyBoard for this purpose.

I was looking for the circuit diagrams to forward but have not found them yet.

Hope this helps clear things up a bit.


Jamie Lawson
Controlled Environment Systems Research Facility
School of Environmental Systems
Bovey Bldg
University of Guelph
Guelph, ON Canada
519.824.4120 x54844

----- Original Message -----
From: bionull <abiding@...>
To: handyboard@yahoogroups.com
Sent: Sun, 8 Nov 2009 14:31:20 -0500 (EST)
Subject: [handyboard] Re: Using I2C interface with the HandyBoard - SPI?

While I appreciate Jamie's contribution, which ports it is referring to and how
one would wire to make the division along input and output rather than SDA and
SCL continues to be beyond me.

What I have made more sense of is the SPI_IC.ic code located in files. Does
anyone have prior success with the use of this code or at least know if the
following recommended scheme simply means that I wire the SDA and a 1.2KOhm
resistor to power on MOSI, and SCL to MISO?
Does that make sense to anyone as achieving I2C?

/* Assumes the following connections: MISO is the CLK (Clock), MOSI is the
    SDA (Data), but these are easily changed:
                               SDA  SCL
         .----.----.----.-----.----.----.----.----.
         | -- | -- | SS*| SCK |MOSI|MISO| TX | RX |  Port D
         `----^----^----^-----^----^----^----^----'
           D7   D6   D5   D4    D3   D2   D1   D0

    The port is operated in wire-or mode so pull-up resistors (~1.2KOhm) will
    be needed on the data line */

Apologies for the basic questions,
Brian Dellon
Electrical Engineering Student
The Cooper Union for the Advancement of Science and Art

While I appreciate Jamie's contribution, which ports it is referring to and how
one would wire to make the division along input and output rather than SDA and
SCL continues to be beyond me.

What I have made more sense of is the SPI_IC.ic code located in files. Does
anyone have prior success with the use of this code or at least know if the
following recommended scheme simply means that I wire the SDA and a 1.2KOhm
resistor to power on MOSI, and SCL to MISO?
Does that make sense to anyone as achieving I2C?

/* Assumes the following connections: MISO is the CLK (Clock), MOSI is the
    SDA (Data), but these are easily changed:
                               SDA  SCL
         .----.----.----.-----.----.----.----.----.
         | -- | -- | SS*| SCK |MOSI|MISO| TX | RX |  Port D
         `----^----^----^-----^----^----^----^----'
           D7   D6   D5   D4    D3   D2   D1   D0

    The port is operated in wire-or mode so pull-up resistors (~1.2KOhm) will
    be needed on the data line */

Apologies for the basic questions,
Brian Dellon
Electrical Engineering Student
The Cooper Union for the Advancement of Science and Art