50g

--- In 50g@yahoogroups.com, "al.arduengo" <al.arduengo@...> wrote:
>
> --- In 50g@yahoogroups.com, "Scott" <blueelectron@> wrote:
> >
> > --- In 50g@yahoogroups.com, "x2dydx" <x2dydx@> wrote:
> > >
> > 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
> >
> 
> The cable I built years ago for the 48 series did not have any 
> conversion circuitry.  If I recall correctly there were three 
lines -
>  tx, rx and gnd.  I will look at my 50g on a scope today and try 
to 
> get firm info.
> 
> -Al
>

The 48GX has a true-ish RS232 port, wich inversion/level conversion 
built-in.

--Scott