Schneider Automation Modicon Quantum Ethernet Guia do Utilizador descarregar pdf (Página 83)

Ethernet Developers Guide

840 USE 115 00 Version 1.0

If the remote node is an IP address, or if it’s a name that has been resolved, then

CSample_View tcpip_connect_r

function is called to initiate a connect re

uest to

the remote node. The listen port for the connect re

uest is five hundred and two,

and is defined b

the constant MBAP_LISTEN_PORT in modbus.h. If

tcpip_connect_r

succeeded in initiatin

a connect re

uest, then tcpip_connect_r

chan

es the transmit state to CONNECTING, otherwise it chan

es the transmit

state to IDLE.

The window sockets DLL

enerates a FD_CONNECT event which indicates if the

connect re

uest succeeded or failed. CSample_View OnTcpIpConnect function

processes the FD_CONNECT event. If the connect re

uest succeeded,

OnTcpIpConnect chan

es the transmit state to CONNECTED, otherwise it

chan

es the state to IDLE.

Recall that MFC architectural framework calls CSample_View OnPollInterval

member function to processes WM_POLL_INTERVAL messa

e sent as result of

CMainFrame class processin

a WM_TIMER messa

e. OnPollInterval examines

the transmit state. If the transmit state is CONNECTED, and the user has selected

a transaction t

pe, then OnPollInterval calls CSample_View TransmitUserRe

uest

function.

TransmitUserRe

uest encodes a re

uest based on the transaction t

pe, saves the

current time, and calls CSample_View TransmitMessa

e function. OnPollInterval

uses the saved time to determine when to transmit the next re

uest.

TransmitMessa

e attempts to send a messa

e to the remote side. To send the

messa

e, TransmitMessa

e enters a loop. In the bod

of the loop transmit

messa

e calls the window socket DLL send function. The followin

lists the

outcomes of the send function and the actions taken.

The messa

e was sent successfull

. TransmitMessa

e chan

es the transmit

state to TX_DONE and exits the loop.

Onl

part of the messa

e was sent. TransmitMessa

e reenters the loop.

Send function returns an error indicatin

there is no buffer space within the

transport s

stem. TransmitMessa

e chan

es the transmit state to BLOCKED

and exists the loop.

Send function returns some other error. TransmitMessa

e closes the

connection, chan

es the transmit state to IDLE, and exits the loop.

When buffer space within the transport s

stem becomes available to transmit

messa

es, the window socket DLL

enerates a FD_WRITE event. CSample_View

OnTcpWrite function processes the FD_WRITE function b

callin

TransmitMessa

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