B.2 Limiting And Operating Data Of The Rs232C Data Interface - Mettler Toledo AE Série Mode D'emploi

B.2 Limiting and operating data of the RS232C data interface

Transfer principie:
The transmit lines: have the following characteristics:
These values are valid with a load resistance of at least 3 kΩ. The sources must be designed so that they are protected
against external sources of up to 25 V/0.5 A (of any polarity).
The maximum permissible current in such cases is 0. 5 A. With short-circuit to ground or to another line, maximum permissible
current is also 0. 5 A. With a load resistance of max. 7 kΩ, the amount of voltage at the balance may not exceed 15 volts.
Receiver lines: The input resistance of the circuit should be between 3 kΩ and 7 kΩ. Input idle voltage (bias) should not be
more than 2 V. The receive circuit must be set up for voltages of at least 25 volts. The maximum capacitance of the receiver
circuit and cable may not exceed 2500 pF. Input voltages of -3 V or more negative are interpreted as MARKING / OFF (HIGH).
Such voltages of +3 V and more are interpreted as SPACING / ON (LOW). The absolute values of the voltages do not exceed
25 V. Voltages between -3 V and +3 V are not defined.
Handshake: If the "Data Terminal Ready" line has a voltage of ≥ + 3 V, the 011 data output can transmit results. If the value
is ≤ -3 V, the data output cannot transmit.
If the level changes from positive to negative during a transfer, no more than 2 additional characters will be transferred. If the
level changes back to positive, the transfer is continued.
If the line is not wired up, the data output behaves the same as if the external instrument would indicate readiness.
6
– bitserial
– asynchronous
– one start bit and one stop bit
– voltage-controlled
– 7 bits per character plus parity bit (ASCII)
– negative voltage in the idle conditon
MARKING / OFF (HIGH):
SPACING / ON (LOW):
at least -3 Volt
at least +3 Volt