RS232c in VB6 help

Question

Hey all i am new at this RS232c command sending. This is what the documents has for my Yamaha A/V RX-A2000.

PWR
  [PUT Command] 
     @MAIN:PWR=Parameter
  [GET Command]
     @MAIN:PWR=?
        Operating & retrieving Power state of Main Zone
        Initial Auto Feedback is Available
  [Parameters]
        Standby
          PUT: turining its state to Standby / GET: indicating Standby status.
        On
          PUT: turining its state to On / GET: indicating On status.
        On/Standby
          PUT Only: toggling its status between On/Standby

I am a little confused as to how to send a command like that through the MSComm control.

MSComm.CommPort = 2
MSComm.Settings = "9600,n,8,1"
MSComm.PortOpen = True

If Not MSComm.PortOpen Then
    MsgBox "not opened"
Else
    MSComm.Output = "@MAIN:PWR=On" & Chr(13)

    Do While MSComm.InBufferCount > 0
         Text1.Text = Text1.Text & MSComm.Input
    Loop
End If

Would that be correct?

David

score 3 · Accepted Answer · answered May 17 '11 at 19:13

3

Your code looks kinda right - conceptually anyway - although the setup for the Do While really isn't quite right. See http://support.microsoft.com/kb/194922 for a coding example. (but the ".Handshaking = 2 - comRTS" part should be ".Handshaking = 2") Using events is the more reliable approach to RS232 communication.

See http://www.vbrad.com/article.aspx?id=37 for further guidance.

If your PC has HyperTerminal (or some other TTY program), use that to attempt manual communication with your Yamaha. Hopefully your users manual has some examples you could try. Google on "hyperterminal rs232" for other ideas; such as http://www.connectworld.net/interface-troubleshooting.html. Going the manual route will at least confirm that you can make your PC talk to your Yamaha, and it will help you think about how to write your code.

(Google "hyperterminal substitute windows" for other TTY programs; such as http://www.windowsreference.com/windows-vista/alternatives-to-hyperterminal-in-vista/)

answered May 17 '11 at 19:13

rskar

4,607
25
21

@AngryHacker - You're welcome! And thank you for the article too! – rskar May 17 '11 at 20:36
OK. I'm not sure i even need the Do While in this as i just want to send the command and thats all. All i am looking for is it sending the command and working :o) And sadly the Yamaha had **NO** rs232c examples for it. I had to dig down really really *really* far to even find the rs232 command sheet for it. Not even the company itself had one to provide me! Sheeesh! – StealthRT May 18 '11 at 13:43
@StealthRT: Sadly, the "Control Expansion Terminal" port isn't meant as a consumer item - they intend it for specialized commercial applications. This may sound silly, but maybe you should first figure out how to make an old fashioned rs232 telephone modem dial a number via HyperTerminal (or whatever). At the least, this diversion will give you some experience in device control over rs232. Just Google "hayes modem commands", hook up an old modem, and give it a whirl. At least modem help is available lots of places. – rskar May 18 '11 at 16:21
Thanks for your reply. However, i am not new to RS232c - i'm just new to the way this is being commanded. I'm used to sending hex or numbers to a device, not words :o) so thats why i was a tad bit confused. – StealthRT May 18 '11 at 18:50

score 2 · Answer 2 · answered May 17 '11 at 19:20

2

The code is sound but has a small flaw. Note this code:

MSComm.Output = "@MAIN:PWR=On" & Chr(13)

Do While MSComm.InBufferCount > 0
     Text1.Text = Text1.Text & MSComm.Input
Loop

In you send some data, then immediately expect to see a response. The code will not enter the Do loop because there will be nothing to read as of yet.

So, either check for .InBufferCount after a small pause or adopt a different approach. I typically have a timer check the port every 200 ms or so (depending on urgency). You could also respond to the OnComm event, but this event has been known to ratchet the CPU usage to 100% if there is too much data going through. It sounds like you'll be dealing with a small set of data, so you should be ok with either approach.

answered May 17 '11 at 19:20

AngryHacker

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325
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OK. I'm not sure i even need the Do While in this as i just want to send the command and thats all. All i am looking for is it sending the command and working :o) – StealthRT May 18 '11 at 13:42
I tried that code out and it did nothing :o(. Have any idea why that would be? – StealthRT May 26 '11 at 02:53
I meant do NOT use this code with the loop. Use a pause instead and then read the port. But to make sure that the device works at all, establish a connection from HyperTerminal or TeraTerm and try it from that. – AngryHacker May 26 '11 at 05:35

RS232c in VB6 help

2 Answers2