Pulse amplitude time
The circuit characteristics (pass band in base band and AC couplings) determine the time has to elapse between each two consecutive level transitions on the line of the serial signal. For the correct operation of the XTR-915, such time must be comprised between 10 and 500μs.
The Data Slicer requires that for at least 1ms before the data themselves, a preamble, composed by a square wave, is transmitted in order to consider reliable the data coming out from the RXD line.
Bit ON/Bit OFF relation
The Data Slicer is optimized for a 50:50 duty cycle. It shall continue to operate, even with bigger distortion and less tolerance to interferences, till a 30:70 or 70:30 duty cycle. It is not possible, therefore, to directly transmit in RS232 logic unless by caring to balance the ratio 1 and 0 in the output, since the duty-cycle could be also of the 90% not permitting thus, the correct operation of the receiver. During the transmitter modulation, while conditioning the input pin [pin 14] by a logic signal, it is recommended not to exceeded the maximum continuous length of 500 μS without transition ON/OFF –OFF/ON ; this in order not to degrade the receiver’s sentivity. It is therefore necessary to modulate by means of specific techniques that allow a low duty-cycle like Manchester, coding from 8 to 12 bits or other suitable techniques. In lack of balancing techniques on the specifications bit, if it is requested to operate with RS232 protocol, it is recommended to utilize a minimum 19.200 bps speed in order to take advantage of the full performances by transmitting, for instance, one byte and its complementary one after the other [balancing over the byte].