Table of Contents
Advertisement
In the Local Mode, data consists of one start bit, eight ASCII formatted information bits, and one
stop bit. The parity is set as indicated by the parity option.
Pin 3 - Received Data (BB)
Signals on this circuit are transmitted by the attached modem to the 7500. This circuit is held in
the MARK state by the modem when data is not being transmitted.
The data from the modem must have one start bit, eight information bits, and at least one stop bit.
Parity is generally ignored in local mode and transported transparently in data mode. (The exceptions
are: 1) the 7500 is always sensitive to the parity of the xon/xoff characters; and 2) the 7500 always
ignores the parity of the Attention sequence characters and the Forwarding characters.) Only ASCII-
formatted data is supported in the local mode. The 7500 recognizes a break signal as previously
described.
Pin 4 - Request-to-Send (CA)
The Request-to-Send lead is used by the 7500 interface to control data transmission. The ON state
of this lead indicates that the 7500 interface is prepared to transmit data. If the Rec.flow option has
been set to eia, an ON indicates that the 7500 is ready to receive data from the attached modem. An
OFF indicates that it is not ready to receive data.
Pin 5 - Clear-to-Send (CB)
The Clear-to-Send lead indicates that the attached modem is ready to receive data (including dialing
information) from the 7500. If the Trans.flow option has been set to eia, an ON indicates that the
attached modem is ready to accept data from the 7500. An OFF indicates that the attached modem is
not ready to accept data from the 7500.
Pin 6 - Data Set Ready (CC)
The Data Set Ready lead will be ON when the associated modem is off-hook. It may also be ON
when the modem is idle, waiting for receipt of an ASCII dialing sequence. Any data call in progress is
ended by the 7500 at the ON to OFF transition of this lead.
Pin 7 - Signal Ground (AB)
This lead provides the common reference level for all signals at this interface. Signal ground is DC
isolated from the power source.
Pin 8 - Received Line Signal Detect (CF)
This pin is also referred to as Data Carrier Detect (DCD).
This circuit will be ON when the attached modem is in Data Mode; that is, it is ready to receive
data from the distant modem. It may also be ON when the modem is idle, waiting for receipt of an
ASCII dialing sequence.
The 7500 ends any data call in progress at the ON to OFF transition of this lead provided the DCD
option is set to follow. The 7500 ignores transitions of this lead when the DCD option is set to ignore.
Pins 12 and 13 - Speed Mode Indicators (CI and CI2)
These leads are read by the 7500 interface to indicate that a multiple speed modem has stepped
down from its nominal (highest) speed programmed via the front panel.
These leads are examined by the 7500 after Received Line Signal Detect comes on and 7500
responds according to the following table, provided the Setup option is set appropriately. The leads are
ignored if the Setup option indicates a single speed modem. Only pin 12 is interpreted if the Setup
options indicate a dual speed modem; both pins 12 and 13 are interpreted if the Setup option indicates
a triple speed modem is connected.
CHAPTER 9: TECHNICAL INFORMATION
133
Advertisement
Table of Contents
