DS276
NOTES:
1. This circuit as shown does not meet the RS-232 requirement for signal levels (high-level output
voltage). However, as most RS-232 receivers will interpret any voltage over 2V as a space this will
normally be of no consequence. Alternatively, VDRV+ can be supplied independently from a higher
voltage supply.
2. The capacitor is charged negatively whenever RXIN is in a marking (or idle) state. When the DS276 is
transmitting marking data and RXIN is spacing the capacitor will discharge towards ground with a
time constant determined by the capacitor value and the value of the load resistance. The value shown
should store sufficient charge for reliable operation up to 20 kbps.
3. RXIN must never be allowed to reach a negative voltage with respect to VDRV- or excessive currents
will be drawn. Therefore, if negative voltage swings are present on RXIN, VDRV- should not be
connected to ground and the circuit shown in Figure 4 should be used.
5 of 11
DALLAS [ DALLAS SEMICONDUCTOR ]
