Northern UTA220/UTA220k - Manual (Page 155)

UTA220/UTA220k
D-7
Interfaces
Receive Clock
In synchronous modes, this output supplies the DTE with
timing information for it to use when reading data from the
UTA. This output is not used in asynchronous mode.
Data Terminal
Ready
This signal is generally supplied by the DTE to indicate that it
is ready to send data.
Ring Indicator
This output pulses high when the UTA detects an incoming
data call on the ISDN.