Page 3 of the manual says...
- Bit ON/Bit OFF relation: the Data Slicer is optimized for a 50:50 duty cycle. It will continue to operate,
even with bigger distortion and less tolerance to interferences, till a 30:70 or 70:30 duty-cycle.
Therefore there is no possibility to directly transmit an RS232 sequence if no action is done to balance the 1
and 0 bits ratio, as the duty-cycle could reach up to 90% preventing the proper performance of receiver. It
will continue to operate, even with bigger distortion and less tolerance to interferences, till a 30:70 or 70:30
duty cycle.The Data Slicer is a comparator with a capacitor on one input. The data goes to both inputs but the capacitor charges to an average of the data. When the data is higher than the average level, the output is high and when the data is lower than the average level, the output is low. The higher baud rate allows less time for the capacitor to discharge which may explain why it appears to work at higher rates but you should not count on this being reliable unless you use byte balancing and rates of 57.600 bps or higher.
- XTR-434
While modulation is applied to TX, conditioning input pin [pin 14] with a logic signal, it is reccomended not
to exceed 200 μs continuous time with no transition from ON to OFF or OFF to ON. This not to downgrade
the RX sensitivity. It is requested that modultation is carried on with techniques that allow a low duty-cycle,
such as Manchester coding, 8 to 12 bit coding or other available technique. If no bit balancing technique is
used, if it is requested to work with RS232 protocol, a minimum speed of 57.600 bps is required to assure
maximum performance, transmitting, for example, one byte followed by the complementary byte (byte
balancing).
Follow the manufacturer's recommendation and use manchester coding (or byte balancing) or find another transceiver. You can find thousands of web pages that describe manchester coding and a search of the forums will turn up Melanie's example code.
Byte balancing means you send each byte twice - once normally but followed immediately by its bitwise complement (i.e. each 1 becomes 0 and vice versa). The sequence is Byte1 ~Byte1 Byte2 ~Byte2...ByteN ~ByteN. On the receiving end, each pair must sum to $FF. If not, there was an error in transmission or reception.
You can see some oscilloscope screenshots showing the effects of the data slicer here...
Bookmarks