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