7700 MultiFrame Manual
7707DT RS-232/422/485 Fiber Data Transceiver
Page - 20
Revision
1.8
4.2.7. Selecting the Serial Data Failsafe Bias
To simplify installation, the 7707DT provides a selectable failsafe bias for balanced serial data signals.
This bias should be active as required by the specific application, and common practice. The failsafe bias
will apply a differ200mV bias to a properly designed RS-485 system while in the idle state. As a
protection feature, the failsafe bias will not become active unless the termination is also active for the
respective channel. The failsafe bias circuit of the 7707DT will function properly over the specified input
common mode range. Selection of the failsafe bias is done using the card-edge interface or through
Vista
LINK
®
control.
To turn the failsafe bias on or off, select the
CTRL
menu item in menu level 1. The 7707DT allows a
failsafe bias threshold to be set independently for each channel. Use the toggle switch to choose the
channel to which the selection will be applied. Press the pushbutton to apply the displayed selection.
CTRL
CH01 to CH04
CH01 to CH04
Range of RS-422/485 channels.
Use the toggle switch to select the
BIAS
menu item and press the pushbutton. The toggle switch may
then be used to turn the failsafe bias on or off. Use the toggle switch to select the desired state then press
the pushbutton to apply the displayed selection and return to menu level 3. You can select other items on
menu level 3, or select the
BACK
menu item to return to menu level 2.
CTRL
CH01 to CH04
BIAS
ON
OFF
ON
The failsafe bias is selected as active.
OFF
The failsafe bias is selected as inactive.
The factory default configuration turns the failsafe bias
OFF.
4.3.
CONNECTING RS422 DEVICES BETWEEN MASTER AND SLAVE
SMPTE Standard 207M defines the electrical and mechanical characteristics of the device interface used
in transferring data and control signals between production and post-production equipment. Each
interface system consists of a single bus-controller (Master) and one or more tributaries (Slaves). The bus-
controller (Master) controls the communication flow to all tributaries (Slaves) connected to it, while a
tributary (Slave) transmits data to an operational device.
A pair of 7707DTs can be configured to interface between a bus-controller (Master) and a tributary (Slave)
if configured as follows:
Controller (Master)
Tributary (Slave)
Signal DB9
Pin#
7707DT
7707DT DB9
Pin#
Signal
Rx-
2
RS422 Out -
RS422 In -
2
Tx-
Tx+
3
RS422 In +
RS422 Out +
3
Rx+
Rx+
7
RS422 Out +
RS422 In +
7
Tx+
Tx-
8
RS422 In -
RS422 Out -
8
Rx-
Table 4-1: Connecting RS422 Signals Between Master & Slave