Table P: Speed Mode Indicator - AT&T 7500 User Manual

CHAPTER 9: TECHNICAL INFORMATION
Table P: Speed Mode Indicator
PIN 12
ON
ON
OFF
OFF
These leads may change state any time after Received Line Signal Detect comes ON including
during the data call.
Pin 18 - Analog Loopback (CN)
This lead will remain OFF.
Pin 20 - Data Terminal Ready (CD)
This lead allows the 7500 interface to control the attached modem. In an idle condition, the 7500
interface holds this lead OFF.
The 7500 interface turns this circuit ON in response to the turning ON of the Ring Indicator lead
for more than 100 msec causing the attached modem to automatically answer a call coming from the
analog network. The 7500 checks for the presence of Data Set Ready, Clear-to-Send, or Receive Line
Signal Detect, for a timeout period of 15 seconds. If the 7500 detects one of these leads as ON within a
15-second time period, the analog call is connected. If the ZCA option is ON, the 7500 generates a Call
Request Packet to the network. This Call Request Packet contains a called address of 10 zeros. If the
ZCA option is OFF, the 7500 will provide the user with access to Local Mode. If the timeout period is
exceeded, the 7500 returns to its idle state (Data Terminal Ready OFF).
This lead also turns ON in response to receipt of an incoming call. This prepares the modem to
accept dialed digits through the EIA interface. The 7500 checks for the presence of Clear-to-Send for a
timeout period of 15 seconds. If the 7500 sees Clear-to-Send ON within this time period, it answers
the call. If the timeout period is exceeded, the 7500 rejects the call and returns to its idle state (Data
Terminal Ready OFF). Autodial modem control commands and responses are data from the 7500's
perspective and are not processed differently from any other customer data.
This lead turns OFF for a minimum of 1 second at the termination of a data call. Incoming calls are
not accepted until after circuit DTR has been OFF for 1 second.
Pin 21 - Remote Loopback (RL)
This lead will remain OFF.
Pin 22 - Ring Indicator (CE)
An ON signal appears on this lead when the modem detects a call coming from the analog
network. This signal may or may not toggle in step with analog 20 Hz ring bursts. The 7500 correctly
interprets the meaning of this signal in either case. The 7500 ignores ON signals less than 100
milliseconds.
Pin 25 - Test Mode
This lead indicates the attached modem is in a test mode. The 7500 does not accept incoming calls
when this lead is ON. The OFF to ON transition, however, does not cause a call in progress to be
disconnected because this is normal in a test mode.
134
PIN 13
ON Remain at Nominal (Highest) Speed
OFF Drop Back One Speed From Nominal
Drop Back One Speed From Nominal
ON
OFF Drop Back Two Speeds From Nominal
ACTION