Data communication apparatus detecting interrupt requests through data error detection

A facsimile apparatus receives data from a transmitting station and is provided with a capability for determining when an interrupt request signal has been received from another station. It is first judged whether an error has occurred in received image information on one line. If an error occurrence is detected, its time period is then measured. If the error period coincides with the output time period for a prescribed interrupt request signal, it is determined that an interrupt request signal has been received. Further, it may additionally be determined whether the coincidence has occurred a plurality of times in succession thereby affirming the reception of an interruption request signal.

BACKGROUND OF THE INVENTION 
The present invention relates to a data communication apparatus and, more 
particularly, to a data communication apparatus, such as a facsimile 
apparatus, which is capable of detecting an interrupt request signal, 
e.g., a "catch phone" signal without the need for special hardware. 
Among the services provided by NTT (Nippon Telegraph & Telephone Company) 
is a "catch phone" service. This service allows an interrupt call with a 
station B while the own station is communicating with another station A. 
More specifically, when the own station is dialed by the station B while 
communicating with the station A, a prescribed call signal (interrupt 
request signal) is sent to the own station from an exchange. If a person 
at the own station manipulates the hook button in response to this call 
signal, the station B is connected to the own station, and a prescribed 
holding signal is sent out to the station A from the exchange. If the 
person at the own station manipulates the hook button again upon 
completion of the communication with the station B, the station A is again 
connected to the own station. 
In the following description, the two stations (station A and own station) 
which are presently communicating with each other will be referred to as 
"transmitting station" and "receiving station", respectively, and a 
station B which tries to make interrupt communication will be referred to 
as "interrupt station". 
The specifications of the call signal and the holding signal used in the 
catch phone service are as follows: 
Frequency: 400.+-.10 Hz 
Output level: not more than -16 dBm 
Tone-on time: 70.+-.10 ms 
Tone-off time: 70.+-.10 ms 
Period: 4 or 8 sec (generally, 4 sec). 
A waveform of these signals is shown in FIG. 7. 
To receive the catch phone service in the case of a facsimile apparatus 
connected to a telephone circuit to communicate of image information, the 
facsimile apparatus may be provided with a means for detecting the call 
signal employed in the catch phone service, and circuits may be switched 
in response to the detection of the call signal. 
This type of facsimile apparatus is disclosed, for example, in Japanese 
Patent Application Laid-Open No. Sho. 62-216584. The disclosed facsimile 
apparatus is constructed such that, when a call signal of the catch phone 
service is sent to a receiving station (or transmitting station), an 
interrupt station is connected to the receiving station upon reception of 
the call signal. A holding signal is sent out from an exchange to a 
transmitting station (or receiving station), which was interrupted in the 
midst of communication, as described above. However, since general 
facsimile apparatuses do not have a capability of detecting this holding 
signal, the transmitting station (or receiving station) is placed in a 
no-signal state, so that this station disconnects the circuit after the 
lapse of a predetermined time. Therefore, the facsimile apparatus of the 
above publication is designed such that the receiving station (or 
transmitting station) automatically dials the transmitting station (or 
receiving station) with which it previously communicated, upon completion 
of the interrupt communication. 
Japanese Patent Application laid-Open No. Sho. 64-86660 discloses a 
technique in which a receiving station (or transmitting station) that is 
in communication with an interrupt station performs a restoring operation 
on a station previously communicated with, before a predetermined time has 
elapsed from the start of the interrupt communication. By virtue of this 
restoring operation, the station of the previous communication will not 
release the circuit even during the interrupt communication. 
In either of the above-described cases, hardware, e.g., a filter, for 
separating the catch phone call signal from a communication signal, such 
as image information signal, is needed to detect the call signal. This 
makes the construction of the data communication apparatus complicated. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a data communication 
apparatus which is capable of detecting a catch phone call signal without 
the need for special hardware. 
A data communication apparatus according to the invention is characterized 
by performing the following judgments: whether an error has occurred in 
received data such as image information during its reception, and whether 
a detected period of error occurrence is coincident with the output period 
of the prescribed interrupt request signal. For example, the error is a 
decoding error as prescribed in CCITT, T5. 
It is an additional feature of the invention that a judgement is made as to 
whether the above coincidence has been detected a predetermined number of 
times in succession. 
When an interrupt request signal, e.g., a catch phone call signal, is 
superposed on data such as image information, an error occurs in the data 
because of a difference in frequency between the data and the interrupt 
request signal. Accordingly, if the period of the error occurrence 
detected as described above is the same as the output period of the 
interrupt request signal, it can be judged that an interrupt request 
signal has been received.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described below in detail with reference to 
the accompanying drawings, by way of embodiments in which the invention is 
applied to a facsimile apparatus. 
FIG. 2 is a block diagram showing the hardware construction of a facsimile 
apparatus according to a first embodiment of the invention. In the figure, 
a reader 1 for reading an original document and a recorder 2 for 
outputting received image information are connected to a communication 
controller 3. Also connected to the communication controller 3 are an 
operating unit 4 consisting of various operating buttons used for 
operating the facsimile apparatus, a display for displaying the status, 
etc. of the facsimile apparatus, and a tone generator. The communication 
controller 3 is connected to a modem 5. The modem 5 is connected to a NCU 
6, which is in turn connected to a telephone circuit. 
The communication controller 3, which has a microcomputer, executes various 
operations required for the facsimile apparatus and operations shown in 
FIGS. 3 and 4. 
Various kinds of protocol signals and image information are sent out to the 
circuit via the communication controller 3, modem 5 and NCU 6, or input to 
the communication controller 3 from the circuit via the NCU 6 and modem 5. 
The operation of the facsimile apparatus according to the first embodiment 
will be explained below. The features of the present invention resides in 
the construction of a receiving station that receives image information. 
FIG. 3 is a flowchart showing a basic operation of a receiving station. 
First, it is judged in Step S1 whether a call (ordinary call other than a 
catch phone call) has been received from a transmitting station. If the 
judgment is affirmative, the circuit is connected to the apparatus in Step 
S2, and a predetermined protocol pre-processing is executed in Step S3. 
In Steps S4 and S5, reception of image information and a predetermined 
protocol post-processing are performed respectively. Thereafter, the 
circuit is disconnected in Step S6, and the process returns to Step S1. 
The received image information is printed out at a predetermined timing, 
although not illustrated in the figure. 
FIG. 4 is a flowchart showing an interrupt process that is executed when it 
is detected that an error has occurred in image information of one line in 
Step S4 of FIG. 3. The image information error can be detected by use of 
known techniques, e.g., the ECM mode and parity check. 
First, it is judged in Step S11 whether a catch phone call signal detecting 
timer (hereinafter referred to simply as "timer"), which will be described 
later in connection with Step S13, has been started. If the judgment is 
negative, a number n is reset to 0 in Step S12. Then, the timer is reset 
and re-started in Step S13 to initiate measurement of time from the 
detection of the data error. Thereafter, the process is terminated to 
return to a previous routine. 
If it is judged in Step S11 that the timer has already been started, the 
timer is stopped in Step S14 to terminate the measurement of time. The 
time that has been detected by the timer is a period of the data error 
occurrence. 
It is judged in Step S15 whether the detected period is the same as an 
output period of the prescribed catch phone call signal. If the judgment 
is negative, the process proceeds to Step S12. 
If the judgment in Step S15 is affirmative, n is incremented in Step S16, 
and then it is judged in Step S17 whether n is equal to or larger than a 
threshold P, that is, it is judged whether it has been judged P or more 
times in succession that the data error period is the same as the output 
period of the catch phone call signal. If the condition n.gtoreq.P is not 
satisfied, the process proceeds to Step S13. If n.gtoreq.P is satisfied, 
it is judged in Step S18 that a catch phone call signal has been received. 
Thereafter, the process is terminated to return to a previous routine. 
FIG. 1 is a functional block diagram of the facsimile apparatus according 
to the first embodiment. 
In FIG. 1, image information transmitted from a transmitting station is 
received by an image information receiving means 11, and then provided to 
an output means 13. 
An error judging means 14 judges whether or not an error has occurred in 
received image information of one line. If an error is detected, the error 
judging means 14 stops a timer 15, and activates a first comparing means 
16. 
When activated, the first comparing means 16 makes a comparison between an 
error period measured by the timer 15 and an output period of the 
prescribed catch phone call signal which is stored in a period storing 
means 17 in advance. If these two periods are coincident with each other, 
the first comparing means 16 causes a counter 18 to count up, whereas, if 
they are not coincident with each other, the first comparing means 16 
resets the counter 18. After the comparison is made by the first comparing 
means 16, the timer 15 is reset and restarted. 
When it is judged by a second storing means 20 that the count value of the 
counter 18 is coincident with a threshold P stored in a threshold storing 
means 19, the second comparing means 20 produces an output signal, which 
is to be a catch phone call signal detecting signal. 
FIG. 5 is a flowchart showing the operation of a facsimile apparatus 
according to a second embodiment of the invention. The flowchart shows an 
interrupt process that is executed when it is judged that an error has 
occurred in image information of one line during its reception in Step S4 
of FIG. 3. In FIG. 5, the same reference numerals as those in FIG. 4 
denote the same or equivalent processes. 
The hardware construction of the second embodiment is the same as that of 
the first embodiment. 
First, it is judged in Step S21 whether or not a detected error is a first 
one. If affirmative, a number n is reset to 0 in Step S12, and thereafter 
the process returns to a previous routine. 
If it is judged that the detected error is not the first one, the number of 
lines existing between the preceding error line and the present error line 
is detected in Step S22. This number of lines is the information 
corresponding to the error period which is detected in Step S14 of FIG. 4. 
It is judged in Step S23 whether the detected number of lines is coincident 
with the number of lines corresponding to the output period of the 
prescribed catch phone call signal. The number of lines corresponding to 
the output period of the catch phone call signal depends upon the 
communication speed. Accordingly, the number of lines that is selected in 
accordance with the communication speed employed is compared with the 
number of lines detected, as described above. If the coincidence is not 
detected in Step S23, the process proceeds to Step S12. 
If the coincidence is detected, n is incremented in Step S16. It is then 
judged in Step S17 whether n is equal to or larger than a threshold P. If 
the condition n.gtoreq.P is not satisfied, the process is terminated to 
return to a previous routine. 
If n.gtoreq.P is satisfied, it is judged in Step S18 that a catch phone 
call signal has been received. Thereafter, the process is terminated to 
return to a previous routine. 
FIG. 6 is a functional block diagram of the facsimile apparatus of the 
second embodiment. In FIG. 6, the same reference numerals as those in FIG. 
1 denote the same or equivalent parts, and descriptions therefor will be 
omitted. 
In FIG. 6, when an error judging means 14 judges that an error has occurred 
in received image information of one line, a present error line data 
storing means 31 is activated to store information about the line in which 
the present error has occurred (e.g., a line number from the top of an 
original document). 
If the error judging means 14 detects an error again, the information 
stored in the present error line data storing means 31 is transferred to a 
preceding error line data storing means 32, and information about the line 
in which the new error has occurred is stored in the present error line 
data storing means 31. 
A number-of-lines detecting means 33 subtracts the previous error line 
number from the present error line number to detect the number of lines 
existing between the preceding error line and the present error line. 
A third comparing means 35 makes a comparison between the number of lines 
detected in the number-of-lines detecting means 33 and the number of lines 
corresponding to the period of the prescribed catch phone call signal, 
which has previously been stored in a number-of-lines storing means 34. 
The number-of-lines storing means 34 stores a plurality of numbers of 
lines (corresponding to the respective periods of the catch phone call 
signal), which are selectively output in accordance with the communication 
speed employed on each particular occasion. If it is detected that the two 
numbers of lines are coincident with each other, the counter 18 is caused 
to count up, whereas, if the coincidence is not detected, the counter 18 
is reset. 
Although in the foregoing embodiments the present invention was described 
by way of one example in which interrupt communication is caused by the 
catch phone call signal, the present invention may be applied to other 
various types of interrupt communication. For example, the present 
invention may be applied to an interrupt communication system employed by 
AT & T, U.S.A. The call signal used in this system comprises two signals 
of 480 and 620 Hz, which are combined together, and is output at 60 IPM. 
Although in the foregoing embodiments it is judged that a catch phone call 
signal has been received when the coincidence between the error period and 
the output period of the catch phone call signal is detected a plurality 
of times in succession, it is, of course, possible to do such a judgment 
when the coincidence is detected only once. 
Further, if a plurality of different periods of interrupt request signals 
are prepared for the comparison with a time interval of an error 
occurrence, it is possible to detect both the catch phone call signal and 
an interrupt request signal other than the catch phone call signal. 
Although in the foregoing description the present invention is applied to a 
facsimile apparatus that performs communication of image information, the 
present invention may be applied to any type of data communication 
apparatuses (e.g., a communication apparatus using a personal computer) as 
long as they are equipped with a modem and perform data communication by 
exchanging prescribed protocol signals. In such a case, data to be 
communicated is not limited to image information, as a matter of course. 
According to the data communication apparatus of the invention, an 
interrupt request signal can be detected without the need for special 
hardware, so that the construction of the data communication apparatus is 
simplified. Further, since it is judged whether the coincidence between 
the error period and the output period of the interrupt request signal has 
been detected a plurality of times in succession, the accuracy of 
detecting the interrupt request signal is improved.