Impulse 3189 - Manual (Page 8)

Card Setup
Sealevel Systems ULTRA-SIO Page 5
Headers E3 (Port 1) and E9 (Port 2) are used to control the RS-485 enable/disable functions for the receiver circuit
and determine the state of the RS-422/485 driver. 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. These header blocks are described in the illustration and table that follow:
Echo
No
Echo 422 485
E3 = Port 1
E9 = Port 2
1
Position 1 ‘Echo’ Echoes the data that is transmitted.
All characters transmitted are
received. (Only relevant in the two
wire RS-485 Mode)
Position 2 ‘No Echo’ Inhibits the data that has been
transmitted. Receiver is off when
transmitter is on. (Only relevant in
the two wire RS-485 Mode)
Position 3 ‘422’ RS-422/485 Driver always enabled
(RS-422 Mode). RTS modem
control signal available on DB-9
connector.
Position 4 ‘485’ RS-422/485 Driver enabled by RTS
or ‘Auto’ enabled. Modem control
signal not available on DB-9
connector.
Interface Mode Examples
RTS
Auto
E8 & E10 E3 & E9
Figure 6 - RS-422
RTS
Auto
E8 & E10 E3 & E9
Figure 7 - RS-485 ‘Auto’ Enabled, with ‘No Echo’