a fresh-girl with puzzle dom

Question

it about serial COM port communications with MSComm,i used ' do{...}while ' to instead of OnComm event,example: byte[] inDate; do { System.Windows.Forms.Application.DoEvents(); }while(com.InBufferCount==0); byte[] inData=new byte[com.inBufferCount]; inDate=(byte[])com.Input; my program is that recieve one byte and send one byte to confirm communication is correct,then recieve the last 292 bytes, but why when the device send bytes to com, the indate only can find 8 bytes?

Administrator · Answer

enhthanks for your replying:)I think you are right!i'll try it with Oncomm event .expecting the more communication with you my mail is seeyounext2000@163.com can we debate with mail? thanks again!

Administrator · Answer

I think that it's because without your messagebox your program runs faster then the bytes are comming in. So if you put a messagebox you have to click 'ok' this takes a few seconds. In this time the bytes are comming in. If you do not put the messagebox your program is executed before all the bytes are in the buffer. So you can not count 292 bytes. Using your code in your first message and setting your com.inBufferSize to 16384 bytes and waiting a few milliseconds is maybe a solution but I don't think it is a good one. I should implement the Oncomm event. It's easy and I never had problems with it. I wrote that the onComm event is executed each time there were 8 bytes in the inputbuffer. But it's better to say: each time there is something comming in. It could be less den 8 bytes or more if the inputbuffersize is more than 8 bytes.

Administrator · Answer

thanks a lot for your respondence! but I set the com.inBufferSize=16384it's enough to read 292 bytes in one times! and if I put a messagebox between communications confirming and the last 292 bytes receiving  after the box clicked the length of inData is 292 it means 292 bytes were read! but why?should there a little waite there? expect your reply again!

Administrator · Answer

If you use the ONComm event it will be executed enough to read the last 292 bytes. Each time the input buffer is filled with 8 bytes the onComm event is executed. You receive also the last 292 but because you do not use the onComm event you are not seeing them. If you alsways expect 292 after confirming just write a loop until you received al the 292 bytes. Maybe something like this: ArrayList l = 0; while (count != 292) { while(comInBufferCount == 0); count += comInBufferCount; inData = com.Input; byte[] inData=new byte[com.inBufferCount]; inDate=(byte[])com.Input for (int i = 0; i< inData.Count; i++) l.add(inData[i]; } Add the end of the 292 bytes the ArrayList will be filled with the 292 bytes. The length of inData is maximum 8 bytes because you are getting maximum 8 bytes from com.Input. So each time you read 8 bytes you have to add them to the array. If you do not always expect 292 bytes add a stopbyte at the end and read the bytes until you read the stopbyte. Or send first the amount of the bytes to this program.