At 15:45 04/03/98 -0500, you wrote:
>Mauro, Chuck wrote:
>
>> BTW: The true EIA spec's for RS232 define a voltage swing even larger
>> than 112V (I forget how large, but it's either 115V or 125V), but PC
>> supplies don't generate anything over 12V (when did they ever?), and the
>> larger delta V just isn't necessary.
>
>The first RS232 was +/- 25V as I recall, I think that the later A & B
>versions switched to +/- 15V, the current RS232C (current?) uses
>+/-12V.

There are several voltages specified at the beginning and end of this
section 2.6:

From the EIA RS-232-C specification, August 1969, page 7, section 2.6:

2.6 The open-circuit driver voltage (Vo) with respect to circuit AB (signal
ground) on any interchange circuit shall not exceed 25 volts in magnitude.
The source impedance (Ro and Co) of the driver side of any interchange
circuit including any cable to the interface point is not specified;
however the combination of Vo and Ro shall be selected such that a short
circuit between any two conductors (including ground) in the
interconnecting cable shall not result in a current in excess of one-half
ampere. Additionally the driver design shall be such that, when thge
terminator load resistance (RL) is in the range between 3000 Ohms and 7000
Ohms and the terminator open circuit voltage (EL) is zero, the potential
(V1) at the interface point shall not be less than 5 volts nor more than 15
volts in magnitude.

Section 6.6 then goes on to state:

6.6 The user is reminded that the characteristics of and equivalent load
(terminator) circuit used to test for compliance with each of the
electrical specifications in section 2 are a function not only of the
parameter under test, but also of the tolerance limit to be tested. For
example, a driver which just delivers 5 volts into a 7000 Ohm test load may
fail the test if the load is reduced to 3000 Ohms, whereas a driver with an
output within the 15 volt limit when driving a 3000 Ohm load may exceed
this limit when driving a 7000 Ohm load. The 5 volt limit should therefore
be tested with a 3000 Ohm load while the 15 volt limit should be tested
using a 7000 Ohm load.

If anyone wants a copy of this specification (I don't have any later ones)
let me know.

Regards

Adrian

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