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© Sealevel Systems, Inc. 3543 Manual | SL9119 9/2022
If your communications package allows the use of Baud rate divisors, choose the appropriate divisor from
the following table:
For this Data Rate
Choose this Divisor
1200 bps
768
2400 bps
384
4800 bps
192
9600 bps
96
19.2K bps
48
38.4K bps
24
57.6K bps
12
115.2K bps
8
230.4K bps
4
460.8K bps
2
921.6K bps
1
Electrical Interface Selection
Each of the ports on the
SIO4-104.485
can be individually configured as RS-422, or as a two wire RS-485
interface. This is a software selectable feature and is found at Base+15. To enable a port for RS-422, simply
write a ‘0’ to Base+15 (this is the power up default). To enable a port for two-wire RS-485 simple write a ‘1’
to Base+15. If the Sealevel Software Windows drivers are used, this is accomplished as a function of the
Device Manager.
RS-485 Enable
RS-485 is backwardly compatible with RS-422; however it is optimized for party line or multi-drop
applications. The output of the RS-422/485 driver is capable of being active (enabled) or tri-state (disabled).
This capability allows multiple PCs to be connected in a multi-drop bus and selectively polled. Half-duplex
two-wire operation is also possible by connecting TX+ to RX+ and TX- to RX- in your cable hood. The enable
to the driver is connected to the UART Request to Send (RTS) line for RS-485 communications. This allows
the RS-485 driver to be tri-stated when inactive on a multi-drop polled network. The software that you are
using must "know how" to enable the driver when it is answering a poll. Failure to correctly utilize the enable
can cause transmitter contention problems preventing operation by any node on the network. If the Sealevel
Systems Windows Software driver is used, a ‘Radio’ style button on the ‘Advanced’ property page under the
Device manager can be selected that will automatically toggle RTS for use as an enable.
