JPS6318482A - Bar code demodulator - Google Patents

Abstract

PURPOSE:To read out a bar code in each word by inhibiting writing when an input permission signal from a first in first out (FiFo) memory is invalid, and when the signal is returned to an input enabled state, outputting a reset bit. CONSTITUTION:The bar width of a bar code counted by a pattern width counter 10 is supplied through the FiFo memory 12 and demodulated by a demodulating circuit 14. When the contents of the memory 12 overflow, an input enabled signal IR outputted from the memory 12 is turned to 'L', a writing signal WE is not outputted from a write control circuit 18, writing in the memory 12 is inhibited and a reset signal RST is outputted from the circuit 18. When the memory is returned to the write enabled state, writing is restarted, a reset bit is added to the output of the memory 12 by the signal RST, so that the circuit resets the data and invalidates the word. Since the bar code constituted of two words is read out in each word in said constitution, the bar code is read out without missing by two scanning, so that the reading efficiency can be improved.

Description

[Detailed Description of the Invention] [1] When input data is lost due to overflow of FiFo, the demodulator is reset and data is input.

[Industrial application field]

The present invention relates to a barcode demodulation device, and particularly to a processing method when a portion of barcode data is lost.

[Conventional technology]

Barcodes are printed on product wrapping paper, etc., and are used to print out product names, prices, and total amounts, and to create sales data. As is well known, barcodes are constructed by combining zero bars and dot bars of multiple widths. An example is shown in FIG. There is a guide bar GB containing two dot bars at both ends and in the center, and between these guide bars there is a numerical value of 9.0.
, 3°, and so on. There are multiple widths for the character bar's dot bars and inner bars (the space between dot bars), such as unit width, double the width, triple width, etc. - Each value consists of two dot bars and two zero bars. be done. A wide space is placed before and after the bar group, and this, together with guide bars at both ends, indicates the beginning and end of the bar group.

A common method for reading barcodes is to scan a group of bars with a beam of light, photoelectrically convert the reflected light, and check the width of each pulse of the resulting rectangular wave signal. Laser scanners are sometimes used for scanning with light beams, and in this case, the scanning light is constantly generated during operation, and when the product is placed on the laser scanner with the barcode printed side facing down, it will be scanned by the laser light. The code is read. In this case, the scanning trajectory of the bar group by the laser beam is not constant, and may deviate from the horizontal line passing through the center of each bar, be above or below it, be diagonal, or be partially missing. A laser scanner is equipped with a polygonal mirror that rotates at high speed and performs repeated scanning, and the scanning locus each time is different, and the bar group may be scanned completely apart. However, when an item is placed on or passed over a laser scanner, a number of scans of light traverse the groups of bars, which produce a code reading output.

Such a scanning method in which the scanning light trajectory is irregular eliminates the need for accurate positioning of the product during reading, and can improve operability.

When the scanning light trajectory crosses the bar group, it first enters the space portion, then enters the guide bar CB at the tip, enters the subsequent character bar, and so on. The width of each pulse of a rectangular wave obtained by photoelectrically converting reflected light is measured by a counter that counts clocks. FIG. 3 shows an example of this measurement circuit.

10 is a bar width counter, and the barcode signal shown by BO2 in Fig. 4 (reflected light is photoelectrically converted, amplified, and shaped)
is input, the clock CLK is counted during each of the H (high) level and L (low) level periods of this rectangular wave, and the counted value indicates the length of each H and L level period. In FIG. 4, this count value is 100.25.23, . . . . Since there is a wide space at the tip of the bar group, the pulse width in this part is large and the counter 10 overflows. The detection circuit 16 detects this and the FiFo
A signal S1 is applied to the write control circuit 18 of the memory 12.

The FiFo memory 12 has a capacity of about 64 words and functions as a buffer. In other words, the laser scan is quite fast, and each word (count values such as 25, 23, etc.) is generated every 0.5 μs, but the demodulation circuit 14 generates one word every 0.5 μs. It can only process at a speed of /3. Therefore, each word generated in one scan is buffered in the memory 12 and sequentially processed in the modulation circuit 14.FiF
o Once data has accumulated in the memory 12 (in this example, 64 words have accumulated), no more can be written, so the input enable signal IR is sent.
is set to L level to notify that writing is not possible.

The write control circuit 18 outputs the write signal WE to the FiFo memory 12 only while the signal IR is at H level, and when the signal S2 indicating the rise and fall of the barcode signal BC3 is input after the overflow signal S1 arrives. . F
When the signal WE is input, the iFo memory 12 takes in the count value of the counter 10 at that time and writes it to the address indicated by a pointer (not shown).

The counter IO outputs its count value at the rising/falling edge of the barcode signal BC3, and also resets itself and starts the next counting.

[Problem that the invention seeks to solve]

Since the capacity of the FiFo memory 12 is approximately 64 words, if a large number of narrow pulses occur in succession, the demodulation circuit 14
The processing cannot be completed in time and the FiFo memory 12 becomes full. Therefore, the memory 12 sets the input enable signal IR to L level and prohibits input. The data whose input is prohibited will be lost, and the barcode demodulation output with missing data will result in an error.

In the conventional system, if input is prohibited (IR=L), the control circuit 18 does not raise the write signal WE after that, starts the next scan, a space is detected, and if the overflow signal S1 is input and IR is H, BO2 is output. WE is generated at the rising/falling edge of .

However, in this conventional method, if input inhibition occurs at the beginning of a group of bars, all subsequent data will be lost. A barcode consists of two words, with one word in the first half of the center guide bar and the remaining one word in the second half. If input prohibition occurs in the first half, the data in the second half will also be lost, but this is a waste. Laser scanning is not always performed horizontally, but may also be performed diagonally, so in the first scan, input was prohibited in the first half, but not in the second half, and in the second scan, input was disabled in the first half. It is also possible that input was prohibited in the second half, although it was normal. If any part of the data is missing, all subsequent data will be discarded.In the above case, it is impossible to read both times, but it should be divided into words, and if input is prohibited, only that word will be discarded. If you do so, it will be readable even in the above case.

The present invention focuses on this point, and aims to improve the barcode reading rate by optical scanning by making code data readable in word units.

[Means for solving problems]

The present invention comprises a bar width counter (10) for determining the width of each bar of a barcode, a FiFo memory (12) in which the counted value of the counter is sequentially written, and a barcode for reading out the memory and decoding the barcode. demodulation circuit (14), and F
While receiving the input enable signal (III) from the iFo memory, a write control circuit (18) is configured to output a count value write signal (WE) of the bar width counter to the FiFo memory at each rise/fall of the barcode signal. In the barcode demodulator equipped with the write control circuit, an input enable signal (IR) is input.
indicates that input is not possible, but if it returns to allow input, a write signal (WE) is output at each rise/fall of the barcode signal, and at this time, a reset signal pit (RST) is output to the FiFo memory. and the barcode fj [
1 circuit (14) is configured to reset the word if there is a reset signal bit (RST) in the FiFo memory read data.

[Effect]

According to this configuration, a barcode consisting of two words can be extracted word by word, so that the reading rate can be improved.

〔Example〕

As shown in FIG. 1, in the present invention, the write control circuit 18 is provided with a function of generating a bit for reset R3T when IR becomes L and WE is not raised. As shown in FIG. 2, this reset signal R3T is IR=L and B
This continues from when WE is not generated at the rise/fall of O2 until when IR=H and WE is raised at the rise/fall of BO2. That is, in the present invention, even if IR=L, WE is not raised at all until an overflow is detected, but if IR=H, WE is raised at the rise/fall of BO2. Then, at the first time when the WE generation is restarted, the R3T bit outputted by the control circuit 18 is written into the FiFo memory together with the count value of the counter 10 at that time. The write destination address is the address indicated by the pointer, and the R3T bit is 1 bit added to a predetermined position (for example, the leading edge or trailing #A) of the counter count value data.

The demodulation circuit 14 sequentially converts the data in the FiFo memory 12 (F
(iF, o) in the writing order) and determine whether it is a guard bar or which value it is based on the combination of pulse widths. In the present invention, if the R5T bit is added, the word data is reset (this function is provided to the demodulation circuit).

In this way, it is possible to collect data in word units, and it is possible to read the entire barcode by using data that could not be read in the first half but was readable in the second half, and vice versa, improving the barcode reading rate. Can be done. If the barcode cannot be read, the operator will have to try again to read it, but if the barcode can be read the same number of times, there will be no need for unnecessary operations.

〔Effect of the invention〕

As explained above, according to the present invention, even if the FiFo memory becomes full and becomes unwritable, all subsequent data is not written to the FiFo memory and is discarded, but when it becomes writable again. Writing is restarted from the current data, and at the beginning of the writing restart, a reset bit indicating that writing has become disabled is written together with the data, and in the demodulation circuit, if there is no reset bit (R3T=L
If so, then the word is valid, and if there is a reset bit (R5T=H), then the word is invalidated (reset), so barcode data consisting of two words can be read word by word. It is possible to improve the reading rate.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the operation of Fig. 1, Fig. 3 is a block diagram showing a conventional example, and Fig. 4 is an explanation of the operation of Fig. 3. FIG. 5 is an explanatory diagram of the barcode. In FIG. 1, 10 is a bar width counter, 12 is a FiFo memory, 14 is a demodulation circuit, and 18 is a write control circuit.

Claims (1)

[Claims] A bar width counter (10
), a FiFo memory (12) into which the counted value of the counter is sequentially written, a barcode demodulation circuit (14) that reads out the memory and decodes the barcode, and a signal (IR) that can be input from the FiFo memory. A barcode demodulator includes a write control circuit (18) that outputs a count value write signal (WE) of a bar width counter to the FiFo memory at each rising/falling edge of the barcode signal while receiving the barcode signal. , even if the input enable signal (IR) indicates that input is disabled, if it returns to input enable after that, a write signal (WE) is output at each rising/falling edge of the barcode signal, and at this time, the reset signal bit (RST A barcode demodulation device, characterized in that the barcode demodulation circuit (14) is configured to output a word to a FiFo memory, and the barcode demodulation circuit (14) is configured to reset the word if there is a reset signal bit (RST) in the data read from the FiFo memory.