Control circuit for a segmented display device

A display device which comprises a keyboard for specifying a character to be displayed, a decoder for converting a specified character signal into segment signals corresponding to light emitting segments, and a display section which is provided with a plurality of segment display elements, and which are so arranged as to emit light in accordance with the contents of the segment signals. In this display device, a ROM converts a signal representing a character specified by the keyboard into at least two character component signals corresponding to at least two character components of the specified character and the converted character component signals are supplied to the decoder.

BACKGROUND OF THE INVENTION 
This invention relates to a segment type character display device. 
Recently various forms of control are carried out by a one-chip 
microcomputer. In this case, a display device whose digit divisions are 
each provided with 7-segment light emitting diodes (LEDS) to indicate the 
results of an arithmetic operation in the form of numerals is connected to 
the one-chip microcomputer. Where not only numerals, but also alphabet 
letters and notations are displayed 9-segment or 16-segment LEDS are used. 
An increase in the number of the segments of each digit division of the 
display device or the forms of characters to be displayed naturally 
results in having to enlarge the capacity of a decoder for converting a 
character signal into a segment signal. Since, however, the one-chip 
microcomputer is often already provided with a decoder, an increase in the 
decoder capacity is objectionable. 
SUMMARY OF THE INVENTION 
It is accordingly the object of this invention to provide a display device 
capable of indicating a large variety of characters by applying a small 
capacity decoder. 
To attain the above-mentioned object, this invention provides a display 
device which comprises a signal generator for issuing a signal 
corresponding to a character to be displayed, a circuit for converting an 
output character signal from the signal generator into at least two 
signals corresponding to at least two character components constituting 
the character represented by the output character signal, and a display 
section including a plurality of segment display elements which are 
selectively illuminated according to the output signals from the circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Description is now given with reference to the accompanying drawings of a 
display device embodying this invention. FIG. 1 is a block circuit diagram 
of the display device. Now let it be assumed that the subject display 
device is applied to a data-impressing camera. In this case, a keyboard 10 
is connected to a central processor unit (CPU) 16 through an interface 
circuit 12 and a bus line 14. The bus line 14 is further connected to a 
read only memory (ROM) 18, random access memory (RAM) 20 and decoder 22. A 
camera 24 is connected to the bus line 14 through an interface circuit 26. 
An output signal from the decoder 22 is supplied to a display section 30 
through an interface circuit 28. The display section 30 is formed of six 
digit divisions, each of which consists of 9-segment LEDs. All LEDs of 
each digit division are connected at one end, (for example, anode) to 
corresponding digit division electrodes. The LEDs of the same segments of 
the respective digit divisions are connected at the other end (for 
example, cathode) to corresponding segment electrodes. With a display 
device embodying this invention, the decoder 22 has nine output terminals. 
An output signal from each output terminal is supplied to the 
corresponding segment electrode of the display section 30. An output 
signal from each output terminal of an interface circuit 32 connected to 
the bus line 14 is supplied to the corresponding digit division electrode 
of the display section 30. A broken line block given in FIG. 1 corresponds 
to a one-chip microcomputer. 
Description is now given of the operation of the display device embodying 
this invention. Data to be impressed on a photograph are previously 
specified by operating the keyboard 10. The specified character data are 
stored in the RAM 20. When data are changed from one film frame to 
another, then the serial numbers of the film frames are also specified by 
operating the keyboard 10 and stored in the RAM 20. The display section 30 
is so positioned that light emitted therefrom is projected on a film 
frame. The photographing operation including film exposure and data 
impressing, etc. is carried out in accordance with a program stored in the 
ROM 18 under control of the CPU 16. A character signal is read out from 
the ROM 20 in synchronization with the shutter release of the camera. 
With the foregoing embodiment, each digit division is formed of 9-segment 
LEDs, and can display 2.sup.9 =512 forms of characters. However, let it be 
assumed that it is intended to display ten digits of 0 to 9, twenty six 
English alphabet letters of A to Z and four notations such as +, -, 
"blank" and , namely, forty characters, as shown in FIG. 2. 
The decoder 22 should be supplied with a 6-bit input signal in order to 
display the forty characters. However, a decoder used with a one-chip 
microcomputer applied for the control of a camera generally has an only 
5-bit capacity. However, some of the forty characters can be respectively 
produced by coupling two characters. For instance, the character 6 is 
produced by coupling the character G to that of -, and the character 8 is 
formed by coupling the character of 0 to that of -. When a dummy character 
1 given in the last of FIG. 3A is taken into account, in addition to the 
forty characters, the characters produced by coupling two characters 
together total twelve forms shown in FIG. 3B. For instance Q is formed by 
coupling 0 to the dummy 1. Therefore, the decoder 22 can well serve the 
purpose, if it has a capacity to decode 29 characters shown in FIG. 3A. In 
other words, the decoder 22 has only to be provided with a 5-bit capacity. 
The display device of this invention is so arranged that the characters of 
FIG. 3A themselves are displayed in combination with the blank character. 
With the display device of this invention, therefore, the ROM 18 stores 29 
character signals shown in FIG. 3A. First and second character component 
signals are read out of the addresses in accordance with the character 
signals specified by the keyboard 10. The two read-out character component 
signals are stored in the RAM 20. When any of the characters shown in FIG. 
3A are specified, then the corresponding character signal and blank signal 
are stored in the RAM 20. When any of the characters indicated in FIG. 3B 
is specified then, the corresponding two character component signals are 
stored in the RAM 20. 
When the shutter is released, the first character component signals of the 
first to the sixth digit divisions are successively read out of the RAM 20 
to be decoded. The decoded signals are supplied as segment signals to the 
corresponding segment electrodes of the display section 30. At this time 
the interface circuit 32 issues a digit division-specifying signal to the 
digit division electrodes of the first to the sixth digit divisions of the 
display section 30. Thus the display of the first character component 
signals is carried out throughout the first to the sixth digit divisions. 
Thereafter, the display of the second character component signals is 
carried out similarly throughout the first to the sixth digit divisions. 
The above-mentioned cycle of displaying the first and second character 
component signals throughout the first to the sixth digit divisions is 
repeated. As a result, the characters initially specified by the keyboard 
10 are displayed. 
With the display device of this invention, one character is displayed by 
displaying the two character components thereof in succession, thereby 
making it possible to apply a decoder having a smaller capacity. Further, 
the full display of one character is effected by the successive two 
emissions of light corresponding to two character component signals, 
thereby well serving the purpose simply by conducting a smaller amount of 
current through the display section 30 each time, and consequently making 
it possible to use a driver having a smaller capacity. 
Obviously this invention is not limited to the above-mentioned embodiment, 
but may be practised in various modifications. A combination of two 
character components is not limited to the aforementioned process. In 
other words, the process of combining two character components may be 
varied, provided the same display segment is not represented by the two 
character component signals. The first and second characters may be 
displayed for each digit division.