Casio Naurtech CETerm Ver.5.5 Scripting Guide Bedienungsanleitung PDF herunterladen (Seite 117)

NAURTECH WEB BROWSER AND TERMINAL EMULATION FOR WINDOWS CE AND WINDOWS MOBILE

CETerm Scripting Guide Page 117

5.8.5 Using Single Byte Reads

One pattern which often works well for handling serial port data is to read a

single byte at a time and to accumulate data until a “complete message” can be

processed. Your application and peripheral device will define what a “complete

message” contains, but often messages are terminated by special characters

such as ASCII ETX. When using single-byte reads, you can keep read timeouts

short and optimize responsiveness.

To use this pattern, you would use WaitForEvent with the EV_RXCHAR event

and process the data within your handler. Here is a template for a single byte

read handler

// Serial port data handler

var responseData = [];

var responseState = "PRE_STX";

function MyReadAndProcess( portIndex )

{

var c;

var readTries = 4;

var sp = Device.SerialPort( portIndex );

while (responseState !== "DONE" &&

readTries > 0)

{

c=sp.ReadByte();

if (c < 0)

{

// Read error, try again

OS.Sleep( 20 );

--readTries;

continue;

}

// Reset tries after successful read

readTries = 4;

switch(c)

{

case ASCII_STX:

// Start of response.

responseState = "DATA";

responseData = [];

break;

case ASCII_ETX:

// End of content

responseState = "DONE";

break;

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