JPH0637843A - Data transmitting device - Google Patents

Abstract

PURPOSE:To decide the connection/non-connection states of plural data terminals with the least number of signal lines and in a short time. CONSTITUTION:The input part of a reception buffer which receives the data includes one or plural data terminals 201-20n which contain the pull-up resistances 41-4n, the transmission buffers 11-1n which transmit the data to the data terminals and define an output part as an impedance respectively in the non-transmission state of data, and a pull-down resistance connected to the output part. Furthermore a data terminal connecting device 100 is added to decide whether the data terminals are connected or not based on the voltage of the output part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission device for connecting a terminal such as a portable bar code reader and a host device such as a central processing unit to relay data transmission between the data terminal and the host device.

[0002]

2. Description of the Related Art Conventionally, when a plurality of data terminals are connected to one line, whether or not each data terminal has a connection signal line in order to judge whether they are connected or not.
Alternatively, the above determination is performed by confirming whether each data terminal is sequentially polled with a transmission signal, and sequentially enabling the reception signal and accepting data for each data terminal.

[0003]

However, in the above-mentioned method having the connection signal line, the number of signal lines is increased, and there are problems of cost increase and device size increase.

Further, in the above-mentioned conventional polling method and sequential acceptance method, there is a problem that it takes time to detect a connection when the number of data terminals increases, because it takes time to respond to data.

The present invention is intended to solve such a conventional problem, and an object of the present invention is to provide an excellent data transmission device capable of determining connection of a data terminal in a short time with a minimum number of signal lines.

[0006]

In order to achieve the above object, the present invention provides one or more data terminals having a pull-up resistor at an input of a reception buffer for receiving data.
A transmission buffer that transmits data to the data terminal and sets the output unit to high impedance when the data is not transmitted,
A pull-down resistor connected to the output unit, and a data terminal connection device that determines whether or not the data terminal is connected according to the voltage of the output unit.

[0007]

Therefore, according to the present invention, the connection determination of the data terminal can be made only by the transmission / reception signal line, and the level determination can be performed without depending on the data communication.

[0008]

1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, reference numeral 100 is a data terminal connection device, and 201 to 20n are a plurality of data terminals. Reference numerals 11 to 1n denote transmission buffers, which are connected to the transmission signals and controlled by the selection signals 1 to n, respectively. Further, when the input transmission signal is LOW, the output becomes high impedance. Reference numerals 21 to 2n denote reception buffers, which are connected to the reception signal and select signal 1
To the selection signal n. 31 to 3n are pull-down resistors, which are connected to the output of the transmission buffer 11 to the transmission buffer 1n, respectively.
The selection signals 1 to n are connected from the transmission buffer 11 to the outputs of the transmission buffer 1n, respectively.

Next, the operation of the above embodiment will be described. When the data terminals 201 to 20n are not connected at all, the selection signals 1 to n are all turned off.

When the data terminal n is connected, the power supply voltage of the data terminal n is divided by the pull-up resistor 4n in the data terminal 20n and the pull-down 3n in the connecting device, and the voltage of the connection signal n is divided by that amount. It becomes a piezoelectric voltage. Pull-up resistor 4
Since the relation between the resistance value R1 of n and the resistance value R2 of the pull-down resistor 3n is set to R1 <R2, the connection signal n becomes the Hi level. When the connection signal n becomes Hi, the data terminal connection device 100 turns on the selection signal n, enables the output of the transmission buffer 1n and the reception buffer 2n, and performs data communication with the data terminal n. For other data terminals, the selection signal is turned off and the outputs of the transmission buffer and the reception buffer are set to high impedance.

While data is not being transmitted from the data terminal connection device 100 side, that is, by default, the signal input section A is LOW and the transmission buffer 1n is OFF,
The signal output section B is in a high impedance state. When the data terminal n is connected, the connection signal n shows the power supply voltage of the data terminal n divided by the pull-up resistor 4n in the data terminal n and the pull-down resistor 3n in the connecting device. For example, the resistance 4n has a value 1/10 that of the resistance 3n, and when the power supply voltage is 5V, the voltage of the connection signal n is about 4.5V. Further, in this case, the threshold value for determining the level of the connection signal n is 2.5 V, and the connection signal n becomes the Hi level. On the other hand, if the data terminal n is disconnected,
The connection signal n is at LOW level due to the pull-down resistor 3n. In this way, the connection / non-connection of the data terminal n can be determined by checking the level of the connection signal n while data is not being transmitted.

For other data terminals not selected, connection / non-connection can be determined at any time by checking the level of the connection signal.

[0014]

As is apparent from the above-described embodiment, the present invention makes it possible to determine the connection of a plurality of data terminals only with the transmission / reception signal lines, so that the device can be made inexpensive and compact, and the level can be determined regardless of data communication. This has the effect that it can be performed at any time and instantly.

[Brief description of drawings]

FIG. 1 is a block diagram of a data transmission device according to an embodiment of the present device.

[Explanation of symbols]

 11-1n transmission buffer 21-2n reception buffer 31-3n pull-down resistor 100 data terminal connection device 201-20n data terminal

Claims (1)

[Claims] 1. One or more data terminals having a pull-up resistor in an input section of a reception buffer for receiving data, and a high impedance output section for transmitting data to the data terminal and not when transmitting data. Send buffer to
A data transmission device comprising: a pull-down resistor connected to the output unit, and a data terminal connection device that determines whether or not the data terminal is connected according to the voltage of the output unit.