50g

--- 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