Assuming all level conditioning, etc. is dealt with, you could do the
following:
1. Open the serial port normally.
This gives you ownership of the port and enables the RS-232 transceiver.
2. Reprogram Port G, bits 0 and 1 on the Dragonball so that they are
general purpose IO pins.
3. Read and manipulate the bits directly.
4. Restore Port G and close the port when you are done.
One gotcha that comes to mind is that the serial manager on some PalmOS
versions spits out a character when the port is opened. Otherwise, aside
from voltages/polarity, you could do bit manipulation of the lines.
If the signals are, in fact, readable by a UART you could use a similar
scheme and access the UART directly. Of course, whenever you are bypassing
the OS you have to worry about hardware independence, and etc.
Good Luck
-jjf
-----Original Message-----
From: Patrick Ouellet [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 24, 2000 12:29 PM
To: Palm Developer Forum
Subject: Re: Raw Data on Serial
Ok... I'm not a electronic technician so I might by wrong it may not be used
to
communicate directly to the Bus (I2C).
The simpless way to explain what i need to do is:
I need to control the Tx & Rx pin so that I can
send a 0 or a 1 on Tx... and listen for 0 and 1 on Rx...
without using a FIFO... so it goes.. when I say, not half a second
later or sooner... When I say... go
"Fitzpatrick, Joe" wrote:
> The first issue is signal compatibility. I2C is a three wire buss (SCL,
> SDA, and GND). All data travels on the SDA line, so it needs to be
> tri-state and bi-directional. I2C also normally operates at VCC
(typically
> +5VDC or +3.3VDC).
>
> The external serial port on the Palm meets none of this criteria. Tx, Rx,
> CTS etc. are fixed as inputs and outputs because of the RS-232 line
driver.
> The line driver also provides RS-232 compatible voltages (nominally +/-
> 12VDC).
>
> The SCL line might be able to go directly to one of the GPIO lines, which
> drive interrupts on the Dragonball via a transistor. But, because of the
> transistor (for protection and level adaptability), you cannot use a GPIO
> line (as is) for SDA.
>
> I suppose you could wire up an external circuit to combine Rx, Tx, and
> handshaking to provide a tri-state, bi-directional SDA line. However,
based
> upon your description it is not clear if you system actually uses I2C. I2C
> is synchronous, there is no need for a break or delay. A start condition
is
> a high->low transition on SDA while SCL is high. Then, the address is
> clocked out, followed by a read/write bit. The slave responds with an ACK
> bit, then bytes are exchanged one at a time with an ACK bit after each (no
> ACK from master on last byte of read). A stop condition is a low->high
> transition on SDA while SCL is high.
>
> You can get the Dragonball manual from Motorola and the hardware SDK for
the
> Palm serial port from Palm (you have to sign up for the program).
>
> Good Luck,
> -jjf
>
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