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CHAPTER 9: TECHNICAL INFORMATION
Pin 3 - Received Data (BB)
Signals on this lead are generated by the 7500 in response to data received from the remote data
equipment or to user commands from the attached data terminal. This lead is held in the MARK state
when Received Line Signal Detect is OFF except for user testing and during Local Mode.
In Data Mode, data transmitted to the attached data terminal will consist of one start bit, eight
information bits, and one stop bit. The parity of data received from the network will be transported to
the attached data terminal without alteration.
In Local Mode, data transmitted to the attached data terminal will consist of one start bit, eight
ASCII formatted information bits, and one stop bit. The parity is set as indicated by the parity option.
The break signal consists of binary zero bit transmission for more than 135 msec followed by binary
one bit transmission for more than 100 msec.
Pin 4 - Request-to-Send (CA)
The Request-to-Send lead can be used by the attached data terminal to control data transmission
depending on how the flow control options are set. The ON state of this lead indicates that the
attached data terminal is prepared to transmit data. If the Rec.flow option (Receive Flow Control
option) has been set to eia, this lead will be utilized as follows: ON indicates the attached data terminal
is ready to receive data; OFF indicates the attached data terminal is not ready to receive data.
Pin 5 - Clear-to-Send (CB)
The Clear-to-Send lead is controlled by the 7500 to indicate when data can be received from the
attached data terminal. If the Trans.flow option (Transmit Flow Control option) has been set to eia,
Clear-to-Send will be used for flow control as follows: ON indicates the 7500 is ready to receive data;
OFF indicates the 7500 is not ready to receive data.
If this option has been set to off or xon/xoff, the Clear-to-Send signal will be ignored.
Pin 6 - Data Set Ready (CC)
The Data Set Ready will be ON while power is available.
Pin 7 - Signal Ground (AB)
This lead provides the common reference level for all signals at this interface. Signal ground is
direct current (DC) isolated from the power source.
Pin 8 - Received Line Signal Detect (CF) or Data Carrier Detect
This lead indicates the presence of a data call connection. If the DCD option is set to ignore, the
Received Line Signal Detect lead is ON while power is available, turning OFF for 1 second after a call
has been cleared. If the DCD option is set to follow, the signal on this lead will go ON after a call has
been connected and will go OFF once the call has been cleared.
Pin 9 - Positive Polarity Test Voltage
Pin 10 - Negative Polarity Test Voltage
Pin 18 - Local Loopback (LL)
When this lead is turned ON, the 7500 enters the local loopback test mode. When this lead is
turned OFF, the local loopback is ended.
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