Chapter 5
Serial Data Format for PoqetLink

This chapter briefly explains how PoqetLink works, and gives a detailed explanation of the serial data formats for received and transmitted data. For a detailed explanation of how to use PoqetLink, please consult the PoqetLink User's Guide.

General Description

PoqetLink is a software utility built into PQXT that allows you to transfer files between PQXT and an IBM PC or compatible computer. With PoqetLink, you can also perform file maintenance on a local or remote computer, such as copying, deleting, renaming, printing, or viewing a file.

In order to use PoqetLink, you must attach a PoqetLink cable to the expansion connector at the rear of PQXT. The other end of the cable is then attached to the serial port of your PC for local communications.

A software connection is established between PQXT and the computer by loading the PoqetLink Utilities and VNA software on the PC, and entering the proper command strings on both computers as outlined in the PoqetLink User's Guide.

RS-232-C Interface

DCE vs. DTE

The RS-232-C standard encompasses two methods for devices to provide data transfer. One method is for the equipment to operate as Data Communications Equipment (DCE), and the other method is to operate as Data Terminal Equipment (DTE). The difference between a DCE and DTE is the direction of signals on the pins. That is, an identical signal on an identical pin may be an output on DCE devices, and at the same time an input on DTE devices.

PQXT is configured as a DTE. The pin assignments on the RS-232-C connector of the PoqetLink cable are as shown in Table 5-1.

Table 5-1: Poqet Serial Cable Pin Assignments (DTE) 

        Pin         Function               Mnemonic      Signal Direction
        ---         -------------------    --------      ----------------
         2          Transmit Data          TXD           OUT
         3          Receive Data           RXD           IN
         4          Request to Send        RTS           OUT
         5          Clear to Send          CTS           IN
         6          Data Set Ready         DSR           IN
         7          Signal Ground          GND           --
         8          Carrier Detect         CD            IN
         20         Data Terminal Ready    DTR           OUT
A modem is normally configured as DCE. Pin assignments are shown in Table 5-2.

Table 5-2: Modem Pin Assignments (DCE) 

        Pin         Function               Mnemonic      Signal Direction
        ---         -------------------    --------      ----------------
         2          Transmit Data          TXD           IN
         3          Receive Data           RXD           OUT
         4          Request to Send        RTS           IN
         5          Clear to Send          CTS           OUT
         6          Data Set Ready         DSR           OUT
         7          Signal Ground          GND           --
         8          Carrier Detect         CD            OUT
         20         Data Terminal Ready    DTR           IN
Notice that if the PoqetLink cable (DTE) is connected directly to a PC (DTE) connector, the outputs of PQXT go directly to the inputs of the other PC: Similarly, this direct pin-for-pin connection allows PQXT inputs to connect directly to the other PC: Now consider the case when PQXT is connected to another DTE device, such as the serial port of a PC. If a direct pin-for-pin connection is implemented, it will result in outputs connected to outputs, and inputs connected to inputs. In this case, a "crossover network" adapter must be used to cross over the signals, so that outputs are connected to inputs. The PoqetLink User's Guide gives the required pin assignments.
Copyright (c) 1989, 1990, 1991, 1992 Poqet Computer Corporation. All rights reserved.
Filename: PoqetPC/docs/poqetpc/techref/chapter5.html
Date Created: 13 Jul 96, Last Modified: 13 Jul 96
Created by Bryan Mason - E-Mail: poqetpc<at>bmason<dot>com