Browse Prior Art Database

Multifunction Counter for a Synchronous Data Link Converter

IP.com Disclosure Number: IPCOM000089704D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 4 page(s) / 48K

Publishing Venue

IBM

Related People

Mitchell, MJ: AUTHOR [+2]

Abstract

A counter mechanism is described for use in a synchronous data link converter which couples a data processor multiconductor interface cable to a single conductor or single path communications link. The counter mechanism is remotely settable to provide different count values, and automatically adjusts the converter to the different block length and record length requirements of different input/output devices which may be located at the far end of the communications link. This counter setting and adjustment function is provided in a manner which is transparent to the channel program in the data processor.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 29% of the total text.

Page 1 of 4

Multifunction Counter for a Synchronous Data Link Converter

A counter mechanism is described for use in a synchronous data link converter which couples a data processor multiconductor interface cable to a single conductor or single path communications link. The counter mechanism is remotely settable to provide different count values, and automatically adjusts the converter to the different block length and record length requirements of different input/output devices which may be located at the far end of the communications link. This counter setting and adjustment function is provided in a manner which is transparent to the channel program in the data processor.

Fig. 1 shows the general environment. A data link converter couples a multiconductor data processor channel interface cable to a single conductor or single path data communications link which runs to a remotely located input/output (I/O) device. The data link may be, for example, a telephone line, a radio link, a fiber-optic line or a coaxial cable, the latter being preferred where the I/O device is located at a moderate distance, on the order of several hundred or several thousand feet, from the data processor. The data link converter converts the data from the DC interlocked serial-by-byte format used by the processor to the synchronous serial-by-bit format used by the "single line" data link. This conversion is desirable because the channel interface cable protocols are adequate for limited distances only. The serial-by-bit transmission on the data link, on the other hand, allows efficient movement of information over relatively long distances. Thus, the data link converter is particularly useful in applications, such as distributed processing applications, where 1/0 devices may be located at distances greater than a few hundred feet from the processor.

It is important that the data link converter be program transparent to the processor channel. It is also important that a fairly high data rate should be supported. High speed data transfer can best be achieved if there are few line turnarounds (LTAs) required of the data link.

The data link converter of Fig. 1 operates in accordance with the known synchronous data link control (SDLC) protocol; a modified nonsequenced format is used. Fig. 2 shows the general form of the SDLC frame format used for sending information (either data or control information) back and forth on the serial-by-bit data link. The information field is of variable length. For some frames, the end flag may be omitted.

This article involves a multifunction counter located in the data link converter and an improved data link signaling protocol that enables the I/O device to set the counter so that the data link converter can automatically provide different SDLC frame information field lengths for different kinds of I/O devices. The setting of the counter is accomplished by means of an initial selection sequence, whereby the data link converter initiates...