Browse Prior Art Database

Automatic Serial Printer Switch for an Automotive Diagnostic Technician Terminal

IP.com Disclosure Number: IPCOM000037092D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Cotton, RF: AUTHOR [+4]

Abstract

This article describes an electronic switch mechanism whereby, automatically, the presence of an external printer for an automotive diagnostic technician terminal is detected and serial data is redirected to the external printer.

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Automatic Serial Printer Switch for an Automotive Diagnostic Technician Terminal

This article describes an electronic switch mechanism whereby, automatically, the presence of an external printer for an automotive diagnostic technician terminal is detected and serial data is redirected to the external printer.

The automotive diagnostic technician terminal incorporates a compact printer as it's hard copy device. An external interface is provided which supports a higher speed printer. The printer interface is a serial RS-232 connection.

The automatic serial printer switch disclosed herein is shown in block diagram form in Fig. 1. It consists of isolation resistors 1, 2 and 3, an OR gate 4 and a control element 5. The basic principle of operation is that the serial data is split and routed to both the compact printer and the external printer. The Clear To Send (CTS)

(Image Omitted)

response from both printers is passed through the OR gate back to the host computer, providing a mechanism for the printer in operation to pass status back to the host computer. A control element is provided to disable the serial data path to the compact printer in the event the external printer is detected.

Fig. 2 is a full schematic of the printer switch. In operation three assumptions are made as follows: 1. The host computer is connected to J1.

2. The compact printer is connected at J2.

3. No printer is connected at J3.

The input design of the compact printer does not conform to the full rules of an RS-232 interface. Its interface is designed to operate with a signal excursion of O VDC to +3 VDC (min), as compared with the RS-232 specification of +3 VDC (min).

Data Terminal Ready (DTR) pin 4 (J1) is set to a high level indicating that the computer is ready to send data. This signal is connected back to the computer via pin 6, Data Set Ready (DSR), which some serial driver software requires. DTR is also connected directly to the external printer connector pin 6 (J3), and to one end of R5. R...