Specifications

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ADMS 44.22 Installation and Operation Manual
INSTALLATION
2.9 Controlling Multiple ADMS 44.22 Units
2.9.1 Multi-drop RS-232
Multiple ADMS 44.22 units can be connected to and controlled from a sin-
gle serial RS-232 port by connecting the serial ports together in parallel with a
duplex or multiplex RJ-11 modular telco adapter, such as the Radio Shack 279-357
or 279-433 adapters. An example of the cabling required for a two-unit setup is
shown below.
When this ‘multi-drop’ RS-232 configuration is used, each ADMS 44.22 unit
connected to the multi-drop port must have a unique Unit ID that is greater than 0.
When the Unit ID is > 0 the RS-232 transmitter remains in a high-Z state (discon-
nected from the RS-232 bus) until the unit is sent a command. When the unit
receives a command it enables its RS-232 transmit line, responds to the terminal,
then immediately returns to the hi-Z state to prevent transmit bus conflicts with the
other ADMS 44.2 connected to the serial port. Since Terminal Echo from the ADMS
44.22 is automatically disabled on units whose Unit ID is > 0, enable local echo in
your terminal application to see the characters as you type them.
When the unit ID = 0, the unit sends out automated terminal responses when-
ever the status of the unit changes. If a unit with ID = 0 is used in a multi-drop con-
figuration, transmit bus contention may arise when communicating with units with
ID > 0, resulting in dropped or corrupted status data from Unit 0. Therefore ID = 0
should be used only when one unit is connected to a single serial port.
2.9.2 USB RS-232
Alternatively, multiple units can be controlled from a single USB port using a multi-
port USB to RS-232 adapter. In this case, each ADMS 44.22 unit is connected to its
Multi-Drop RS-232 Cabling
Multi-Drop RS-232 Cabling