Facsimile apparatus

A high speed, high performance facsimile apparatus having an image data storing function is disclosed. In the apparatus, coders, decoder and other structural elements are connected to a system bus. Delivery of instructions from a processing unit to the various structural elements in the system, return of responses from the structural elements to the processing unit, and exchange of image data between the structural elements are effected over the system bus, so that a single processing unit executes both the control and the input and output of image data.

BACKGROUND OF THE INVENTION 
The present invention relates to a high speed, high performance facsimile 
apparatus which has an image data storing function. 
Prior art facsimile systems have generally been constructed with either one 
of two different designs, one directed toward cutting down cost and size 
and the other toward enhancing speed and performance. A low cost, small 
size facsimile apparatus is usually provided with a single processing unit 
(microprocessor) which executes various kinds of control and processing 
including compression and restoration of image data, sequence control, 
exchange of data through input/output ports, exchange of image data 
through an image recorder (plotter) and an image reader (scanner), 
communication protocol control, and operator interface control. A 
high-speed and high-performance apparatus, on the other hand, is provided 
with a plotter, a scanner, a data compression/restoration unit and a 
communication control unit which are constructed separately from each 
other. All these independent units are controlled by a processing unit, 
while input and output image data are processed and transferred by another 
hardware without the intermediary of the processing unit. For example, 
concerning the sequence control over various structural elements of a 
facsimile apparatus, it is executed by a processing unit and the transfer 
of image data between the elements is implemented with an exclusive 
high-speed transfer bus or with hardware which interconnects the elements, 
in the latter case the bus connection to the processing unti being 
omitted. Such makes the overall construction of the apparatus complicated 
and bulky. In an apparatus using a certain prior art system, input and 
output of image data to and from a data compression/restoration unit is 
accomplished using a hardware interface and, therefore, definitely 
determined in configuration at the stage of hardware design, thus lacking 
flexibility in meeting a particular application. That is, with such an 
apparatus, it is impossible to flexibly change the sequence and frequency 
of image data transfer between the structural elements for matching them 
to a particular system application. Stated another way, it is difficult to 
use the apparatus for multiple purposes and, therefore, the system lacks 
vertatility. 
Meanwhile, a type of high-speed, high-performance facsimile system known in 
the art is furnished with a store and forward (SAF) function for storing 
and then transmitting image data. In the event of reception of image data, 
the SAF type facsimile apparatus temporarily stores received image data in 
an image data store area and allows them to be outputted as a hard copy 
afterwards through a recorder. Generally, facsimile communications are set 
up based on any of communication systems which are described in CCITT 
Recommendations, e.g. GIII communication system. While a facsimile 
apparatus operates as a receiving station, it sends a digital 
identification signal (DIS) back to a transmitting station as an initial 
identification signal. As well known in the art, the signal DSI serves to 
inform the transmitting station of the performance particular to the 
receiving station, the performance including the minimum transmission time 
specific to the transmitting station. The minimum transmission time is 
defined as a transmission time necessary for transmitting one scanning 
line of image data. 
A prior art facsimile apparatus, even if provided with the SAF function, 
has customarily been designed to inform a transmitting station of a hard 
copy outputting rate of its recorder as the minimum transmission time. 
This gives rise to a problem that since the outputting rate of a recorder 
in general is far slower than the writing rate of a memory and, therefore, 
it is quite probable that the store area for the temporary storage of 
received image data becomes partly emptied, the reception of image data is 
restricted by the slow output rate of the recorder. Such has obstructed 
fast and efficient transmission of image data. 
SUMMARY OF THE INVENTION 
It is therefore a first object of the present invention to provide a 
facsimile apparatus which is versatile in system application, small size, 
high speed, and excellent in performance. 
It is a second object of the present invention to provide a facsimile 
communication system which is capable of transmitting image data within a 
short period of time. 
It is another object of the present invention to provide a generally 
improved facsimile apparatus. 
In one aspect of the present invention, there is provided a facsimile 
apparatus comprising a processor, a bus connected to the processor, a 
store connected to the bus for temporarily storing image data, an image 
data input device connected to the bus for inputting visible images as 
image data, a communication control connected to the bus for transmitting 
and receiving image data to and from a communication line, coders 
connected to the bus for compressing the inputted image data, a decoder 
connected to the bus for restoring the received image data to original 
image data, and an image data output device connected to the bus for 
outputting the restored image data as visible images. 
In another aspect of the present invention, there is provided a facsimile 
apparatus comprising a processor, a bus connected to the processor means, 
a store connected to the bus for temporarily storing image data, an image 
data input device connected to the bus for inputting visible images as 
image data, a communication control connected to the bus for transmitting 
and receiving image data to and from a communication line, coders 
connected to the bus for compressing the inputted image data, a decoder 
connected to the bus for restoring the received image data to original 
image data, and an image data output device connected to the bus for 
outputting the restored image data as visible images. The processor is 
constructed to apply instructions to the store, the image data input 
device, communication control, coders, decoder and image data output 
device over the bus, and control the image data input device, 
communication control, coders, decoder and image data output means upon 
reception of responses from those units, whereby image data inputted by 
the input device are transmitted to the communication line as compressed 
image data, while image data received over the communication line are 
outputted by the output device. The bus is constructed to cause image data 
to be transferred between the processor, store, image data input device, 
communication control, coders, decoder, and image data output device. 
In another aspect of the present invention, there is provided a facsimile 
apparatus comprising a processor, a bus connected to the processor, a 
store connected to the bus for temporarily storing image data, an image 
data input device connected to the bus for inputting visible images as 
image data, a communication control connected to the bus for transmitting 
and receiving image data to and from a communication line, coders 
connected to the bus for compressing the inputted image data, a decoder 
connected to the bus for restoring the received image data to original 
image data, and an image data output device connected to the bus for 
outputting the decoded image data as visible images. The coder is 
constructed to compress image data inputted by the image data input device 
or image data stored in the store without being compressed, the compressed 
image data being stored in the store or transferred to the communication 
control to be transmitted. The decoder is constructed to restore image 
data which are received by the communication control or image data which 
are stored in the store without being restored to original image data. 
In another aspect of the present invention, there is provided a facsimile 
apparatus comprising a processor, a bus connected to the processor, a 
store connected to the bus for temporarily storing image data, an image 
data input device connected to the bus for inputting visible images as 
image data, a communication control connected to the bus means for 
transmitting and receiving image data to and from a communication line, 
coders connected to the bus for compressing the inputted image data, a 
decoder connected to the bus for restoring the received image data to 
original image data, an image data output device connected to the bus for 
outputting the restored image data as visible images. The processor is 
constructed to apply instructions to the store, image data input device, 
communication control, coders, decoder and image data output device over 
the bus, and control the image data input device, communication control, 
coders, decoder and image data output device upon reception of responses 
from those units, whereby image data inputted by the input device are 
transmitted. The bus is constructed to cause image data to be transferred 
between the processor, store, image data input device, communication 
control, coders, decoder, and image data output device. The coder is 
constructed to compress image data inputted by the image data input device 
or image data stored in the store without being compressed, the compressed 
image data being stored in the store or transferred to the communication 
control to be transmitted. The decoder is constructed to restore image 
data which are received by the communication control or image data which 
are stored in the store without being restored to original image data. 
In another aspect of the present invention, there is provided a facsimile 
communication system in which image data are transmitted based on a 
transmission time which at the beginning of transmission of image data is 
sent to a transmitting station as a minimum transmission time which is 
contained in an initial identification signal for a communication control 
procedure. The system comprises a store having a capacity large enough to 
temporarily store a predetermined unit of image data, and a recording 
device for outputting received image data as visible images. The apparatus 
at the time of reception of image signals sending to a transmitting 
apparatus a minimum transmission time which is a time corresponding to an 
image data writing rate of the store when the store means is not full and 
corresponding to an image data outputting rate of the recording device 
when the store is full. 
In accordance with the present invention, a high speed, high performance 
facsimile apparatus having an image data storing function is provided. In 
the apparatus, coders, decoder and other structural elements are connected 
to a system bus. Delivery of instructions from a processing unit to the 
various structural elements in the system return of responses from the 
structural elements to the processing unit, and exchange of image data 
between the structural elements are effected over the system bus, so that 
a single processing unit executes both the control and the input and 
output of image data. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following detailed 
description taken with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While the facsimile apparatus of the present invention is susceptible of 
numerous physical embodiments, depending upon the environment and 
requirements of use, a substantial number of the herein shown and 
described embodiments have been made, tested and used, and all have 
performed in an eminently satisfactory manner. 
Referring to the drawings, a facsimile apparatus in accordance with the 
present invention is shown and includes a central processing unit (CPU) 10 
having a system bus (CPU bus) 12. An image reader or scanner 18 and an 
image recorder or plotter 20 are connected to the system bus 12 via 
handshake logics (HSL) 14 and 16, respectively. As described later in 
detail, the CPU 10 totally controls the whole apparatus at a high level 
and may advantageously be implemented with a microprocessor, for example. 
The system bus 12 includes a data bus, an address bus, and a control bus. 
The scanner 18 serves to read images on a document and input the image 
data into the apparatus as bit data and, for this purpose, it includes 
various systems for reading such as a document feed system, an optical 
system, an illuminating system, and electrical system. The plotter 20, on 
the other hand, is an image recording device adapted to produce the image 
data, or bit data, as a hard copy and fulfills such a function by means of 
a recording medium feed system, a recording system, etc. Also connected to 
the system bus is an operating section 22 which interfaces an operator to 
the apparatus. As shown, the operating section 22 includes a keyboard 24 
which is connected to the bus 12 via a keyboard interface 26, and a 
display 28 which is connected to the bus 12 via a display control 30. 
Characters to appear on the display 28 are generated in dot patterns by a 
character generator 31 which is also connected to the system bus 12. 
In this particular embodiment, an image data processing section comprises 
two coding and compressing units (coders) 32A and 32B and an image 
processor 36 which are also connected to the system bus 12. Each of the 
coders 32A and 32B removes redundancy from image data and, thereby, 
compresses them using a plurality of data compression algorithms such as 
modified Huffman and modified READ coding systems. The decoder 34 
functions to decode compressed image data to restore original data and has 
a plurality of restoration algorithms. Various kinds of image processing 
such as reduction, enlargement and line density conversion are assigned to 
the image processor 36. A communication control unit (CCU) 38 is connected 
to the system bus 12, while an external communication line 39 
interconnects a remote receiving apparatus to the CCU 38. The CCU 38 
executes communication protocol to the receiving apparatus according to, 
for example, the GIII standard of CCITT Recommendations, as well as 
modulation and demodulation. 
A DRAM 40, a CMOS RAM 41 and a ROM 42 are connected to the system bus 12 as 
storages of the apparatus. As described later, the DRAM 40 defines a store 
area mainly adapted to store visual data such as image data and coded data 
as well as data stored in a floppy disk 50, which will be described. This 
particular store area is usable not only as a data buffer between the 
various units which are connected to the system bus 12, but also as an 
area for storing and transferring (SAF) visual data. Further, a part of 
the same area is used as FIFO adapted for interunit transfer rate 
adjustment. The CMOS RAM 41 stores supervisory data associated with the 
system and, in this particular embodiment, backed up by a battery or like 
spare power source. A control program which the CPU 10 is to run and 
various fixed data are stored in the ROM 42. A clock 44 is connected to 
the system bus 12 and comprised of a calender clock unit adapted for the 
management of time and date. The information output from the clock 44 is 
transferred from the display control 30 in the operating section 22 to the 
display 28 to be displayed. Such information may be superposed on visual 
information as desired after being transformed into dot patterns by the 
character generator 31. An interruption control 46 is connected to the 
system bus 12 in order to control various kins of interruption to the CPU 
10. 
The apparatus of the present invention is capable of allowing the various 
units to exchange data directly at a high-speed over the system bus 12. 
Such direct memory addressing (DMA) is effected by a DMA control 48. The 
previously mentioned floppy disk 50 and a fixed disk 52 constitute a file 
memory device in the illustrative system. The disks 50 and 52 are 
connected to the system bus 12 via an interface 54 and a disk control 56 
and used to store visual data, for example. 
During tansmit mode operation, image data read by the scanner 18 are 
directly transferred to the DRAM 40 of the apparatus controlled by the DMA 
control 48, that is, without the intermediary of the CPU 10. In the DRAM 
40, the image data are stored in the SAF area. The data stored in the DRAM 
40 are transferred to the coders 32A and 32B, again controlled by the DMA 
control 48. The coders 32A and 32B compress the input data by removing 
redundancy from them using a predetermined algorithm. The coded data 
output from the coders 32A and 32B are returned to the DRAM 40 under the 
control of the DMA control 48 to be temporarily stored in the FIFO area of 
the DRAM 40. 
Assume that the clock 44 which supervises the time of the system has 
reached a time which may have been preset in the CPU 10. Then, the CCU 38 
sets up connection of the apparatus to a receiving apparatus over the line 
39 under the control of the CPU 10. Thereafter, the DMA control 48 reads 
the compressed data out of the FIFO area of the DRAM 40 on a 
first-in-first-out (FIFO) basis while feeding them to the CCU 38. This 
FIFO area functions to match the processing rates of the coder 32A or 32B 
and the CCU 38. The CCU 38, independently of the procedure described so 
far, interconnects the apparatus to the receiving apparatus over the line 
39 controlled by the CPU 10. Then, the coded data output from the DRAM 40 
are modulated by the CCU 38 to be delivered to the line 39. In this 
manner, in a transmit mode operation the image data are rapidly 
transferred over the system bus 12 chiefly controlled by the DMA control 
48. It will be seen that the coder 32A or 32B bifunctions to code those 
image data which are to be transmitted over the line 39 and those which 
are to be stored in the DRAM 40 and floppy disk 50. 
Meanwhile, the CPU 10 executes total controls over the whole system such as 
applying a read command to the scanner 18, a write command to the plotter 
20 and other high-level commands and receiving and processing responses to 
those commands, instructing the coders 32A and 32B to start and stop 
coding operation, supervising data stored in the DRAM 40, controlling the 
DMA control 48, and instructing the CCU 38 to start and stop the 
communication procedure. 
Now, even through protocol may be set up between the transmitting and 
receiving stations by the CCU 38, transmission of image data will be 
disabled if the transmitting station differs from the receiving station in 
any one of the compression system for compressing image data stored in the 
DRAM 40, the line density, and the document size. Then, it is necessary 
for the transmitting station to match itself to the receiving station by 
removing the difference. In accordance with the present invention, such a 
requirement is met by the following procedure. 
First, the image data are read out of the DRAM 40 and transferred to the 
decoder 34 and, then, stored in the DRAM 40 again. Thereafter, the decoded 
data are read out of the DRAM 40 to be compressed by the coder 32A or 32B 
in a specific manner which matches with the conditions of the receiving 
station. The coded data are returned to the DRAM 40 again. Finally, the 
coded data in the DRAM 40 are sent out to the line 39 by the CCU 38. 
Naturally, such data transfer between the various units occurs at a high 
speed under the control of the DMA control 48. Further, the DRAM 40 is 
used for multiple purposes as a buffer memory adapted to match the data 
transfer rates of the decoder 34 and the coder 32A or 32B and to match 
those of the coder 32A or 32B and the CCU 38. 
During a receive mode operation, first the CCU 38 responds to a signal 
coming in over the line 39 by informing the CPU 10 of the reception of 
data. Then, the CPU 38 proceeds with communication control according to a 
predetermined reception control procedure. The received image data, 
although in a compressed format, are applied to the FIFO area of the DRAM 
40 to be temporarily stored therein under the control of the DMA control 
48. Thereafter, the image data are read out of the DRAM 40 to be delivered 
to the decoder 34. The image data decoded by the decoder 34 are returned 
to the DRAM 40 controlled by the DMA control 48 and, then, read thereoutof 
by the DMA control 48 to be produced as a hard copy by the plotter 20. In 
this manner, the decoder 34 serves not only to reproduce image data which 
are received over the line 39 but also to decode image data which are to 
be written into the DRAM 40. It is to be noted that the image data stored 
in the DRAM 40 are held therein at least until that the plotter 20 has 
properly produced a hard copy is confirmed. 
As described above, during a receive mode operation image data are stored 
in the DRAM 40. In parallel with such an operation, image data on a 
document are read by the scanner 18 and stored in the DRAM 40 and, at this 
instant, compression by the coders 32A and 32B and storage of compressed 
data into the DRAM 40 can be performed by simultaneous processing. Another 
capability of the apparatus is that while image data stored in the DRAM 40 
are transmitted with the line density changed, other image data may be 
read by the scanner 18 and written into the DRAM 40. In such a case, one 
of the coders such as the coder 32A will compress image data for 
transmission (here, line density conversion), and the other coder 32B will 
compress new image data to be stored in the DRAM 40. 
An arrangement may be made such that while image data are read by the 
scanner 20, they are compressed by the coder 32A, then the compressed data 
are fed to the DRAM 40 and, at the same time, to the decoder 34 to be 
inverted to non-compressed data, and then the non-compressed data are 
compressed again by the coder 32B based on a compression system which 
matches with the conditions of the receiving station. An arrangement may 
also be made such that when the line density and document size associated 
with the so compressed and stored image data have been decided to differ 
from those of the receiving station, the decoder 34 processes the coded 
data back to the non-compressed data and, then, the image processor 36 
converts the line density and document size again. Conversely, in a system 
having a plurality of decoders, an arrangement may be made such that one 
of the decoders restores image data coming in through the line 39 to 
original image data, while the other restores coded data stored in the 
DRAM 40 to non-compressed data and a coder compresses the non-compressed 
data using a compression system which matches with particular conditions 
of a receiving station. 
Conversion of image data as described above enables image data stored in 
the DRAM 40 to be transmitted with the line density of image data, the 
document size and the compression system matched to those of a receiving 
station. The reconversion of the line density and document size are 
effected by decoding compressed image data stored in the DRAM 40 by means 
of the decoder 34 and, then, applying the decoded image to the image 
processor 36. 
However, as appreciated from the above, the possibility of image data being 
repeatedly transferred over the system bus 12 is increased, reducing the 
throughput of the whole system. From the utilization standpoint, 
therefore, image data to be stored in the DRAM 40 should advantageously be 
conditioned to match with the functions of the other party as far as 
possible. In this particular embodiment, such is implemented with the CMOS 
RAM 41 which is capable of storing information particular to a receiving 
subscriber, i.e. data representative of performance specific to a 
subscriber's facsimile apparatus. As previously stated, the CMOS RAM 41 is 
backed up by a battery or like spare power source to preserve the stored 
data for a long time. As the operator enters a subscriber's number on the 
operating section 22 with the intention of transmitting image data to a 
desired remote subscriber, the CMOS RAM 41 stores it. When the coders 32A 
and 32B and image processor 36 compress image data read by the scanner 18, 
they are supplied with information specific to the subscriber which are 
read out of the CMOS RAM 41 controlled by the CPU 10 so that the image 
data are compressed under particular conditions matching with the 
performance of the remote subscriber's apparatus, e.g. compression system, 
document size and line density. The so compressed image data are stored in 
the data buffer area of the DRAM 40 under the control of the DMA control 
48, as previously mentioned. 
As described above, image data read by the scanner 18 are compressed in 
conformity to functional conditions which are specific to a receiving 
station in order to reduce as far as possible the probability of 
occurrence that image data need to be reconverted before delivered to the 
line 39. Consequently, the chance for image data to be transferred over 
the system bus 12 is decreased, enhancing the data processing throughout 
of the overall system accordingly. For example, DMA controller HD69450 
(Hitach Ltd.) which is a peripheral of micro-CPU 6800 (Motorola) is 
capable of transferring data at the rate of 4 megabytes per second. Where 
a document of a format A4 is scanned at the line density of 8 lines per 
millimeter, the total number of bits in the main scanning direction is 216 
bytes. In a system having an input output rate of 5 milliseconds per line, 
a transfer rate of 43.2 kilobytes are necessary for one line of data to be 
transferred. Since this transfer rate is approximately ninety-two times 
the transfer capacity of the above-mentioned DMA controller, the use of 
such a controller enables data transfer to occur ninety-two consecutive 
times. Hence, the transfer in the illustrative embodiment which only needs 
to occur less than ten times can be realized leaving a sufficient margin 
in the micor-CPU transfer. 
Generally, it is advantageous from economy standpoint that in storage and 
transmission (SAF) of image data the data be compressed at the time of 
storage as well. Heretofore, such storage of image data has been 
implemented using an exclusive compression and restoration unit. In 
contrast, in this particular embodiment, the coders 32A and 32B, decoder 
34 and others are connected to the system bus 12 to replace the exclusive 
compression and restoration unit. That is, a single compressing unit is 
usable for both of compression for transmission and that for storage. Such 
not only simplifies the construction but also efficiently copes with any 
difference in the parameters of compressed data between the transmitting 
and receiving stations. 
As previously described, the apparatus of the present invention is capable 
of storing image data read by the scanner 18 even during a receive mode 
operation, remarkably improving operationability in half-duplex facsimile 
communications. This particular function is impracticable with prior art 
systems or, if practicable, would require an expensive system which relies 
on an intricate construction and overlapping functions. This particular 
embodiment of the present invention realizes such multiple functions by 
means of a simple construction. 
Now, in this particular embodiment, the CCU 38 executes a communication 
control procedure according to a facsimile communication system as 
prescribed by CCITT Recommendations, e.g. GIII. Assume that the 
illustrated apparatus is a receiving station which receives data from a 
remote transmitting station. Upon reception of a signal coming in through 
the line 39, the receiving station sequentially proceeds with phases 1-5. 
As well known in the art, the receiving station at the beginning of phase 
2 sends a signal DIS or a non-standard facilities signal NSF back to the 
transmitting station in order to inform the latter of various functions 
specific to itself. The twenty-first to twenty-third bits of the signal 
DIS are indicative of the minimum transmission time per scanning line. In 
a prior art facsimile apparatus, it has been customary to return A signal 
DIS by setting in those specific bits an allowable reception rate as is 
determined by a recording time per scanning line particular to a recorder 
of the apparatus; a transmitting apparatus selects a particular mode 
matching with the own station's conditions based on the returned 
functional conditions, then sets it in a digital command signal DCS, and 
then sends it to the receiving station. 
In the illustrative embodiment, where the apparatus serves as a receiving 
station and if the buffer area of the DRAM 40 assigned to received image 
data is not full, not the recording rate of the plotter 20 but the writing 
rate of the DRAM 40 is set in the twenty-first to twenty-third bits of the 
signal DIS as the previously mentioned reception rate. The twenty-first to 
twenty-third bits are denoted in milliseconds and the storing rate of the 
memory concerned is usually far higher than the image signal transmission 
rate, so that in this case the twenty-first to twenty-third bits are set 
to zero millisecond. Upon reception of the signal DIS, the transmitting 
station selects a particular mode matching with the own conditions based 
on the functional conditions which are contained in the signal DIS, and 
then transmits a digital command signal DIS to the receiving station 
setting the selected mode in the signal. At the transmitting station, 
since the image data read by the scanner 18 are temporarily stored in the 
DRAM 40, image data can be transmitted with the minimum transmission time 
per scanning line set to zero millisecond so long as they are read out of 
the DRAM 40. 
It is not contradictory that even when image data read by the scanner 18 
are directly applied to the line 39, transmission is effected with the 
minimum transmission time of zero millisecond. Fill bits may be inserted 
in compressed image data on a one scanning line basis in order to match 
the transmitting data rate to the inputting rate of the scanner 18. 
Further, where the delivery rate to the line 39 is higher than the 
compressed data generation rate, the store area of the DRAM 40 is apt to 
become empty while the compressed data are read out of the DRAM 40 to be 
transferred to the CCU 38. In such a condition, fill bits may be inserted 
in the image data to be transmitted by the CCU 38. 
Referring to FIGS. 2 and 3, there are shown controls in accordance with the 
illustrative embodiment in phase 4 (end-of-message-transmission 
confirmation procedure) which is based on the GIII multi-page transmission 
procedure. 
The controls shown in FIGS. 2 and 3 are executed at a transmitting or 
receiving station mainly by the CCU 38 under the control of the CPU 10. At 
a transmitting station, as messages in one page of document are fully 
transmitted to a receiving station in phase 4, a multi-page signal MPS is 
sent to the receiving station as a postcommand message and, then, the 
operation returns to phase 2 (200). At the receiving station, as a signal 
MPS, an end-of-procedure signal EOP and an end-of-message signal EOM are 
received during multi-page reception mode (100), if storage of data into 
the DRAM 40 is under way (102), whether the DRAM 40 will have a sufficient 
empty space in its store area when image data in the next page and onward 
are received (104). If such an empty space is available, the operation 
returns to the usual phase 2 (procedure after the setup of a call and 
before the transmission of a message). If the empty space is not 
available, whether a hard copy produced by the plotter 20 has acceptable 
quality is determined (106). 
Thereafter, in this particular embodiment, a mode change request signal MCR 
is transmitted from the receiving station to the transmitting station as a 
post-message response signal, thereby requesting the former to change the 
mode. At this instant, if the quality of the hard copy produced by the 
plotter 20 is acceptable, the receiving station sends to the transmitting 
station a mode change request positive signal MCR-P and, if not, then a 
mode change request negative signal MCR-N (112). Then, the control at the 
receiving station returns to phase 2. Here, an actual output rate at 
which the plotter 20 produces image signals as a hard copy is selected to 
be the minimum transmission time which is to be contained in the signal 
DCS to be sent from the receiving station to the transmitting station as a 
response of an initial identification signal DIS in phase 2. 
Meanwhile, as shown in FIG. 3, the transmitting station which has sent the 
signal MPS (200) decides whether the received data contains a message 
confirmation signal MCF, a reception failure retrain request signal RTN or 
the like (202). If none of them is contained, then whether a signal MCR-P 
or MCR-N is contained is determined (204). If none of them is contained, a 
disconnect command signal DCN is transmitted (206) to disconnect the line 
(208). If the signal MCR-P or MCR-N is contained, the operation returns to 
phase 2. That is, the transmitting station receives another initial 
identification signal to see the minimum transmission time of the 
receiving station again. Based on the result, the transmitting station 
sets up an image data transmission rate. Specifically, the transmitting 
station sees that the DRAM 40 at the receiving station is full and, 
therefore, matches its transmission rate to the hard copy output rate of 
the recorder of the receiving station. Such prevents the data buffer area 
of the DRAM 40 of the receiving station from overflowing and allows the 
recroder to sequentially record image data while gradually increasing the 
empty space. As the empty store area increases in the DRAM 40 of the 
receiving station, the control at the receiving station returns to phase 2 
at a control step 104. At phase 2, zero millisecond is set again in the 
signal DIS and sent back to the transmitting station so that transmission 
of image data can be resumed at the writing rate of the DRAM 40. 
As described above, in this particular embodiment, a receiving station has 
the DRAM 40 capable of storing a large amount of image data and, so long 
as the DRAM 40 is not full, not the outputting rate of the plotter 20 but 
the writing rate of the DRAM 40 is transmitted to the transmitting station 
to cause the latter to send out image data at the writing rate. It follows 
that even if the outputting rate of the plotter 20 is lower than the image 
data transmission rate, image data can be transmitted rapidly to increase 
the transmission efficiency of the whole system. 
Generally, while a recorder having a high output rate is complicated and 
expensive, the semiconductor technology now under rapid progress is ready 
to yield a semiconductor memory having a greater capacity such as the 
order of 1 megabits at a lower cost. Using such a large capacity 
semiconductor memory, it is possible to construct a facsimile apparatus 
which is simple in construction and small in size as a whole system and, 
despite the use of a low-speed image data recorder, achieves a 
transmission rate which is equivalently comparable with or even higher 
than that of an apparatus of the type using a high-speed recorder. In 
addition, a memory adapted for storing and forwarding (SAF) image data, 
i.e. DRAM 40 in the illustrative embodiment, is constantly utilized with 
efficiency. 
In summary, a facsimile apparatus in accordance with the present invention 
has various advantages as enumerated below. 
(1) A single processing unit suffices for both the control and the input 
and output of image data because the delivery of instructions from the 
processing unit to various structural elements in the system, return of 
responses from the structural elements to the processing unit, and 
exchange of image data between the structural elements are performed 
through a system bus. The system, therefore, features unprecedented 
flexibility in application and the apparatus is small in size and high in 
speed and performance. 
(2) Since coders, a decoder and other structural elements are connected to 
the system bus, they are usable not only for transmission purpose but also 
for storage purpose. This also enhances a small-size, high-speed and 
high-performance apparatus design. 
(3) So long as an image data store at a receiving station is not full, 
image data can be transmitted to the receiving station at a writing rate 
of the store so that the image transmission time is shortened. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.