50g

--- In 50g@yahoogroups.com, "x2dydx" <x2dydx@...> wrote:
>
> > Just to be clear re: serial port of 50g.  It is not a true RS232-
> > standard device.  It's a 3.3V TTL signal (noninverted).  There 
> > should be a third-party cable soon if you don't want to make one 
> > yourself.
> > 
> > --Scott
> >
> 
> Hi Scott, I don't mean to beat this subject to death but I assumed 
that 
> the serial output from the calculator would be RS232.  I really 
> appreciate you giving the heads up that it is not standard RS232 
> but "3.3V TTL signal (noninverted)," however I don't know the 
> ramifications of that difference.  So I guess the question is, are 
the 
> two signals compatable and the interface as simple as building a 
cable, 
> or is there some signal incompatabilities that require additional 
> electronic signal processing (for example an inverter) in order to 
> interface the calculator to a standard RS232 connection?
>

Hi,

With the 50g, a mark (1) is +3.3V and a space (0) is 0V.  For 
standard RS232 (going from memory and recalling some specs for the 
48GX), a mark is -(3 to 25)V and a space is +(3 to 25)V, with +/- 
10V being pretty typical for a typical RS232 charge-pump circuit 
(MAX232 chip, etc.) being driven by +5V.  What does this mean?  
First, it means that the signal has to be inverted and scaled to at 
least +/- 5V (space/mark, respectively--notice the inversion).  I do 
not know what the "fault" tolerance is on the 50g's serial port 
(i.e., can it handle +/- 25V?).

For some of the older calculators with serial ports, according to 
comp.sys.hp48, there was an interface cable that "stole" some of its 
power from the hardware handshaking lines in order to power the 
conversion circuitry (MAX232, etc.).  WITH THE 50G, ONE OF THE PINS 
TAPS DIRECTLY TO THE BATTERY TO PROVIDE +6V TO POWER THE CONVERTER, 
if desired.  I believe that if the converter is left on the 
calculator and draws power it may drain the batteries.  I have not 
verified if this battery voltage is "switched" when the unit is on--
I wouldn't count on that.

From a programming point of view, since the 50g has a USB port also, 
if you want to send data through the serial (not RS232 as indicated) 
port, you will need to set system flag -78.  In order to use Conn4x, 
be sure to clear flag -78.  Also, be sure to set the "wire" transfer 
option.

HTH,
Scott