Manual Number: 00750-006-5
Page 6
ULTRA-485 Manual
Header E3:
This header is used to control the RS-485 enable/disable functions for the receiver
circuit. The RS-485 “Echo” is the result of connecting the boards receiver inputs to the transmitter
outputs. Every time a character is transmitted, it is also received by the board. This can be beneficial
if your software can handle echoing (i.e. using received characters to throttle the transmitter) or it
can confuse your system if it does not. The ULTRA-485 provides a jumper block (E3) to enable or
disable this function.
The selection at E3 should follow the selection made at E5 if ‘No Echo’ is desired. If Echo suppression
is not desired, 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 6: Header E3 RS-485 Receive Mode
