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Integrators’ Reference Manual for ViewStation EX, ViewStation FX, and VS4000
106
www.polycom.com
Both endpoints in Pass-Thru Mode 
—Two stations set to Pass-Thru 
Mode behave as a null-modem between their respective externally 
connected devices. Data from the RS-232 port on one endpoint is 
pushed through the call to the other endpoint, and then transmitted 
to the endpoint’s RS-232 port. The data channel speed is 
dynamically allocated. The maximum data flow rate is based on the 
bandwidth of the call. 
Because data throughput has priority over video throughput, video 
bandwidth may be restricted to support data requirements. Audio 
is not compromised.
Far-site endpoint in Control Mode
—If the near site is set to 
Pass-Thru Mode and the far site is set to Control Mode, the far-site 
device acts as a slave under the control of the device connected to 
the near-site endpoint’s RS-232 port.
The following table summarizes the port operation based on the 
RS-232 mode configured by each endpoint.
Flow Control
The ViewStation EX, ViewStation FX, and VS4000 support 
hardware flow control. Users should make sure that hardware flow 
control settings are consistent between the system and the external 
devices on both sides of the connection. 
Table 5-2.  RS-232 Control and Pass-Thru Modes
Near-Side Mode
Far-Side Mode
Resulting Operation
Control
N/A
Near-side CLI 
(Command Line 
Interface)
Pass-Thru
Control
The near-side controls 
the CLI of the far side
Pass-Thru
Pass-Thru
The data is passed in 
full-duplex mode from 
the near-side RS-232 
port to the far-side 
RS-232 port