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