User Manual

Card Setup
Sealevel Systems ULTRA-485 Page 6
Header E3 is used to control the RS-485 enable/disable functions for the
receiver circuit. The RS-485 ‘Echo’ is the result of connecting the receiver
inputs to the transmitter outputs. Every time a character is transmitted, it is also
received. This can be beneficial if the software can handle echoing (i.e. using
received characters to throttle the transmitter) or it can confuse the system if the
software does not. The selection at E3 should follow the selection made at E5 if
‘No Echo’ is desired. If Echo suppression is not desired then leave the jumper in
the ‘422’ position. Also note, the modem control inputs (DSR, DCD, CTS) are
only valid when Header E3 is in the 422 mode. These header blocks are
described in the illustration and table that follow.
RTS
422
AUTO
E3
RX
AUTO
Receiver automatically enabled/disabled
RTS
Receiver enabled by UART RTS signal
422
Receiver always enabled
Figure 5 - Header E3 RS-485 Receive Mode