Method for the operation of an interface circuit between a central portion and local portions of a subscriber termination module of a digital time multiplex telecommunications network

In a subscriber termination module for coupling a plurality of subscriber termination lines of a digital time multiplex telecommunications network, lines coupling a central portion and local portions individually allocated to at least one subscriber termination line are selectably utilized for the transmission of status setting information to the local portions for setting different operating conditions and for serial transmission, that is, successive transmission of information to be supplied to the individual local portions as well as for simultaneous information transmission from the local portions to the central portion, that is, parallel information transmission.

The present invention relates to a method for the operation of interface 
circuits between a central portion and local portions of a subscriber 
termination module of a digital time multiplex telecommunications network. 
Such interfaces play a roll particularly in integrated services 
telecommunication systems in which speech as well as data signals are 
transmitted. In the subscriber termination modules of such 
telecommunication systems, special components are included as local 
portions which in turn are allocated to at least one terminal equipment, 
and cooperate with a central control as a central portion. A subscriber 
termination module comprises, for example, eight such special components, 
which are respectively responsible for two subscriber termination ports. 
Between such components and the central control are, on the one hand, 
setting information to be transmitted from the central control to the 
component, and on the other hand status signals to be transmitted from the 
components to the central control with regard to the subscriber 
termination lines of the subscriber termination ports. 
In the case of a known architecture of this kind, the interfaces between 
the central portion and local portions are formed by line groups in which 
the lines by way of which the setting information is transmitted to the 
local portions are separated from the lines on which status information 
reaches the central portion from the local portions. 
A task of the invention is to provide a method which allows a reduction in 
the expenditure of lines and makes possible servicing of the individual 
local portions by the central portion with as few instruction cycles as 
possible wherein all local portions are monitored simultaneously for 
better dynamic use of the central portion. 
In accordance with a method of the kind referred to above, which in 
accordance with the invention is characterized in that the lines coupling 
the central portion and the local portions are selectively utilized on the 
one hand for the transmission of information from the central portion to a 
respective local portion and on the other hand for the transmission of 
information provided by the local portions simultaneously to the central 
portion as well as for the status setting information to be supplied to 
the same extent by the central portion to the local portions, in that for 
a serial information transmission in which the central portion 
successively provides information to the local portions, of the said lines 
such as are allocated to the individual local portions, for the selection 
of the local portion and such as are jointly provided for the local 
portions are utilized for this serial information transmission, and for a 
parallel information transmission in which the local portions 
simultaneously provide the same type of information to the central portion 
the lines jointly provided for the transmission of status setting 
information to the local portions and the individually provided lines are 
utilized for the transmission of the said same type of information to the 
central portion. 
In accordance with a further embodiment of the invention the setting 
information transmitted by way of the joint lines to the local portions 
respectively appears in the form of combinations of distinguishable line 
status on the totality of this line taking into consideration the 
succession of the occurrence of line status change in the generation of 
these line status. It is thereby possible to transmit more distinguishable 
setting information than corresponds to the number of lines provided.

In FIG. 1 a component ALAP (analog line audio processor) of a subscriber 
termination module which is allocated to two subscribers, and 
correspondingly is coupled to two interface components SLIC 0 and SLIC 1, 
which are responsible for the so-called BORSHT functions, that is for the 
supply (battery), over-voltage protection (over-voltage), the ringing 
supply (ringing), signalling supervision (supervision), the two-wire to 
four-wire conversion (hybrid), and the line testing (testing). Component 
ALAP in turn is responsible for the analog-digital conversion of speech 
into digital signals, limiting of the speech band in a PCM filter, as well 
as for the time slot allocation and furthermore represents the interface 
for signaling and setting data to a group control Ctr. 
A subscriber group serves a plurality of subscribers, for example, 16, in 
which case 8 of components ALAP are present. 
The method in accordance with the invention concerns the operation of 
interface circuits between group control Ctr as a central portion of a 
subscriber termination module and the components ALAP as local portions of 
this subscriber termination module. 
Based on the type of operation in accordance with the invention only three 
lines are needed for the connection of the group control Ctr with a 
component ALAP by way of which all setting information and indication 
values for the indication of the respective appurtenant subscriber 
termination lines are transmitted. 
These are the lines CS, DIO and DCLK. Line CS is an individual line leading 
to component ALAP. Under the precondition that seven further such 
component units are present within a subscriber termination module, as 
stated, seven further such lines CS are present. Lines DIO and DCLK are 
multiple lines which form a connection of control Ctr with further 
components ALAP, not shown. 
In accordance with the invention these lines are used for the transmission 
of two types of different information. Line CS serves on the one hand in 
the transmission of setting information from control Ctr to component ALAP 
as a selectable line for one of the components ALAP coupled to Ctr and on 
the other hand for the transmission of indication information from 
component ALAP to control Ctr, which provide information on the line 
condition of the subscriber termination line. 
In one case line DIO is utilized as a serial data line for data 
transmission from component ALAP, in another case it serves the 
transmission of status setting information which is provided by control 
Ctr and serves to interogate the individual line conditions of the 
subscriber termination lines involved. 
Finally, line DCLK is alternatively utilized for the transmission of a 
clock signal for the above-mentioned serial data tranmission from 
component ALAP to control Ctr or nevertheless also for the transmission of 
status setting information from control Ctr to component ALAP. 
The individual possible operating conditions will next be explained in 
greater detail with the aid of FIG. 2. 
Status 0 which indicates the rest condition is characterized by the binary 
line condition combination CS=1; DIO=1; DCLK=1. 
Departing from this rest condition status 1 can be reached by wayof the 
transition from CS=1 to CS=0, in which line DIO serves for the serial data 
transmission to component ALAP or as the case may be line DCLK serves for 
the transmission of the clock signal. Both lines represent in this 
condition a serial interface since they are placed in succession at the 
disposal of the individual components ALAP. which is achieved in that 
status 1 is set for the individual ones of these components in succession 
with CS=0. 
A transistion from CS=0 to CS=1 causes a return to status 0, that is, the 
rest condition. 
As is further shown in FIG. 2, two successions of states can be reached 
from status 0, namely status 2a through 2c or as the case may be status 3a 
through 3c. 
Status 2a is reached through the transition of DIO=1 following DIO=0 with 
unchanged line conditions CS=1 and DCLK=1. In this state an interrogation 
takes place concerning the loop condition of the subscriber termination 
line coupled to the subscriber termination circuit SLIC 0 or, as the case 
may be, component unit ALAP. The corresponding loop condition signals are 
transmitted in this state by wayof line CS to control Ctr, in which case 
this line is thus utilized in accordance with the second alternative. 
Transmission of loop condition signals also takes place simultaneously by 
way of the remaining lines CS which provide a connection between control 
Ctr and components ALAP which are not shown, which signifies that a 
parallel interface is now realized. 
If a change of state from DIO=0 to DIO=1 takes place from this state 2a on 
line DIO, then state 0 is again reached. 
However, if the line condition combination determining state 2a changes to 
the effect that DCLK=1 changes to DCLK=0, then state 2b is reached, in 
which an interrogation takes place of the subscriber termination line 
coupled to the subscriber termination circuit SLIC 0 or as the case may be 
of all corresponding subscriber termination lines coupled to the remaining 
components ALAP with regard to the presence of an earth connection. In 
this case too, the corresponding earth connection signal is transmitted 
from component ALAP to control Ctr by way of line CS. A transition of the 
line condition DIO=0 to the line condition DIO=1 leads from this state to 
state 0. 
State 2c is reached from state 2b through the line condition change from 
DIO=0 to DIO=1. Special supplemental information can be sent in this 
condition by way of line CS to control Ctr. Also from this condition, a 
jump can be made directly to state 0, by a change in line condition from 
DCLK=0 to DCLK=1. 
The second series of states of state 3a through state 3c relates to 
corresponding interrogations and the provision of information in 
connection with the second subscriber allocated to component ALAP or as 
the case may be the corresponding subscriber termination circuit SLIC 1. 
State 3a is reached from state 0 by changing line condition DCLK=1 to 
DCLK=0. As shown in FIG. 2, the same line condition combinations DIO=0 and 
DCLK=0 occur for the selection of the line conditions of state 2b and 
state 3b. The discrimination as to which of the two conditions is 
correspondingly set up, depends on whether in the preceeding history of 
the setting of this line condition combination, departing from state 0 a 
condition change DIO=1 following DIO=0 had occurred or a line condition 
change of DCLK=1 to DCLK=0.