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Browse Prior Art Database

Asynchronous Bidirectional Interface

IP.com Disclosure Number: IPCOM000049233D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 66K

Publishing Venue

IBM

Related People

Larner, RA: AUTHOR [+3]

Abstract

An interface structure and protocol is provided that meets the following objectives: 1. Narrow (few lines) = low cost implementation 2. Simple (straightforward protocols) = low cost implementation 3. Asynchronous operation = one side of the interface can disconnect to execute a long time internal operation not requiring the interface, thus freeing the interface for other usages, end then re-connect when appropriate. 4. Parallel (with parity), bidirectional data transfuser equals high transmission rate with error checking.

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Asynchronous Bidirectional Interface

An interface structure and protocol is provided that meets the following objectives: 1. Narrow (few lines) = low cost implementation

2. Simple (straightforward protocols) = low cost implementation

3. Asynchronous operation = one side of the interface can

disconnect to execute

a long time internal operation not requiring the interface,

thus freeing the interface for other usages, end

then re-connect when appropriate.

4. Parallel (with parity), bidirectional data transfuser equals

high transmission rate with error checking.

The disclosed interface could be used in many applications within a data processing system, input/output subsystem, or an otherwise logically implemented machine for the controlled bidirectional transmission of data. Although the transmission of data is bidirectional, there is a master to slave structure within the interface. The organization and usage of the bidirectional bus "strobes" are considered to be the novel portion of this interface.

Fig. 1 shows the overall functional connection structure of the interface in use. The multi-drop portion of the interface connects from the adapter to first device and propagates to the second device.

The radial portion separately connects from the adapter to esch device. The adapter is the host system to device connection means and becomes the master element in the master to slave configuration. Only two devices are shown, but the interface can be extended to additional devices by continuing the multi-drop propagation portion and adding an extra radial portion for each device. Both the multi-drop portion and several radial portions can be physically contained in a single, common, flat cable.

Interface Line Definition and Usage
A. Multi-drop portion

1. Data Bus (bidirectional) - 8 bits plus odd

parity

a) from adapter - transmit commands and write

data to device

b) from device - transmit status, sense data and

read data to adapter.

2. Data Bus Strobes (unidirectional)

a) Al - Adapter to device

Informs drive that command byte or write

data byte is on the bus

Acknowledges to device that a status, sense or

reed data byte was received and accepted.

b) F1 - Device to Adapter (primary)

Informs adapter that a non-last byte of a

sense or read data sequence is on the bus

Acknowledges to adapter that a non-last

byte of a command or write data sequence

1

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has been received error free.

c) F2 - Device to Adapter (secondary)

Informs adapter that status byte is on the bus.

Informs adapter that last byte of sense or

read data sequence is on the bus.

Acknowledges to adapter that last byte of

command or write data sequence has been

received error free.

Acknowledges to adapter that non-last byte of

command or write data sequence received in error.
B. Radial Portion (unidirectional)

1. Select - Adapter to device

Dedicates the data bus to a connection between

adapter and that device.

Gates on F1 and F2 and data bus of that device

2. Attention - Dev...