JPS6145271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data transfer system. To explain in more detail, in a device where multiple CRT terminals are connected to one host computer, for example, when outputting data with a printer, it is possible to connect this one printer to each CRT terminal. This relates to a data transfer system that can be used jointly.

First, the conventional technology was converted into CAD (Computer Aided)
Design) device will be explained as an example. general
In a CAD device, multiple CRT terminals are connected to one host computer. In such devices, there are cases where it is desired to extract the contents of the CRT screen using a printer or other hard copy means. Therefore, peripheral devices such as a hard copy device or a message printer device are connected to the CRT terminal, but these peripheral devices usually do not have multiplexing functions of their own. For this reason, each CRT
Prepare the same number of peripherals as the number of terminals,
These peripheral devices are connected to each terminal, but this is very wasteful.

The device shown in FIG. 1 was conceived based on the above considerations. In the figure, 1 to 4 are terminals, and 5 is a peripheral device as described above. 6 is a dedicated multiplexer that appropriately switches connections between each terminal and peripheral equipment. In the apparatus shown in FIG. 1, signals can be transferred in parallel from each terminal 1 to 4 to the peripheral device 5 by the function of the dedicated multiplexer 6. Therefore, one peripheral device can be shared by multiple terminals, and there is no need to provide a large number of peripheral devices. However, the device shown in Figure 1 has drawbacks such as the number of terminals that can be connected is limited by the number of connectors on the dedicated multiplexer, and the total cable length connecting the dedicated multiplexer 6 and each terminal becomes long. .

The present invention has been made in view of the above points.

To summarize the present invention, each terminal has an I/O circuit consisting of a priority discrimination circuit and a plurality of buffers.
An interface is provided, and multiple signal lines are connected in series through all the interfaces, that is, in a daisy chain, and control signals and data signals are transmitted through each signal line. This is a data transfer system in which data is transferred between the one peripheral device and each terminal by transferring data.

The present invention will be explained in detail below using the drawings.

FIG. 2 shows one of the data transfer systems according to the present invention.
FIG. 3 is a diagram showing a connection example, and FIG. 3 is a diagram showing a configuration example of an I/O interface used in the data transfer system according to the present invention. In FIG. 2, 1 to N are terminals (eg, CRT terminals), and 10 is a host computer.
Each of the terminals 1 to N as described above is connected to a host computer 10 and mutually transfers data. In such a device, one peripheral device 5 such as a printer is connected. The operation of each signal shown in FIG. 2 will be explained in FIG. 3.

FIG. 3 is a diagram showing an example of the configuration of an I/O interface used in the data transfer system according to the present invention, in which 11 is a priority determination circuit;
and b are batshua. Here, to explain the meanings of the signals shown in Figures 2 and 3, STR is a data transfer start signal, STROBE is a strobe signal for each data, ACK is an acknowledgment signal from a peripheral device, and DATA is a transfer signal. Data, Ea, and Eb are buffer enable (Buffer enable)
enable) signal. In addition, the above start signal,
The strobe signal and acknowledge signal are collectively referred to as control signals. The transfer data (DATA) is also referred to as a data signal.

In the data transfer system of the present invention, an interface having the configuration shown in FIG. 3 is provided for each terminal. All these interfaces are then connected in a daisy chain configuration as shown in the figure. Specifically, as shown in FIG. 3, a plurality of signal lines are provided so as to pass through each interface in series. Note that in FIGS. 2 and 3, the configuration of each terminal main body is omitted, and only the interface added to this terminal is depicted. This is because the configuration of each terminal is not related to the gist of the present invention.

The operation of the apparatus shown in FIGS. 2 and 3 constructed as described above is as follows. In FIG. 2, consider the case where data from terminal 2 is transferred to peripheral device 5.

(1) First, start signal SRT of terminal 2
When @ is made active, the priority determination circuit 11 compares this SRT@ signal with SRT1 from terminal 1, determines that terminal 2 became active first, and at the same time outputs SRT.
2 signal is activated and sent to terminal 3. Similarly, a start signal is transmitted from terminal 3 to final terminal N. In addition,
Even if terminals 1 and 2 become active at the same time, the 2 side has priority.

(2) The buffer enable signal Ea becomes active by the priority determination circuit 11, and the a side of the buffer is selected.

Next, the terminal 2 repeats the cycle of (DATA@setting...→STROBE@active...→ACK@taking) based on the normal data transfer procedure, and returns SRT@ to inactive when the data transfer is completed. This allows each
The SRT signal becomes inactive and the operation is completed.

(3) If, for example, a terminal with a higher number than terminal 2 becomes active before terminal 2, no ACK signal is sent back to terminal 2. After each terminal sends the first STROBE signal, it determines whether the transfer request is successful or not depending on whether the ACK signal is returned within a certain period of time.

Note that although the explanation has been given above using a CAD device as an example, the present invention is not limited to this example. That is, the present invention can be used as a multiplexing means for Centronics and other devices having parallel and serial communication formats.

In this way, according to the present invention, one peripheral device can be shared by multiple terminals, so the system can be configured at low cost, the total cable length can be shortened, and the number of terminals that can be shared can be freely chosen. You can get a big effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a conventional data transfer system, and FIG. 2 is a diagram showing a configuration example of a data transfer system according to the present invention.
FIG. 3 is a diagram showing an example of the configuration of an I/O interface used in the data transfer system according to the present invention. 1 to 4...Terminal, 5...Peripheral device, 10
...Host computer, 11...Priority determination circuit, a, b...Buffer.

Claims (1)

[Claims] 1. In a device in which a plurality of terminals are connected to a host computer and the plurality of terminals share one peripheral device, each terminal is configured with a priority discrimination circuit and a plurality of buffers. By providing an I/O interface, connecting multiple signal lines through all the interfaces in series, and transferring control signals and data signals via each signal line, A data transfer system that transfers data between peripheral devices and each terminal.