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Hi, I'm no specialist in COM port communication but if you use a COM port you first need to find out on which way to communicate with the device. Means, baud rate, parity, stop bit etc. must fit. It's like a heartbeat: In the tact of the speed you have set when you open the port it will try to read data (or write). If that doesn't fit together then it reads data for example after the sender already sent data (with maybe another speed) and then data in between is lost. Only if sender and receiver are using the exact same parameters the communication will be successful. I don't know "CommRead", but I guess it will already use a loop to get the data you want to have using the number of bytes. Maybe it is the same as in this article, where also the source is mentioned: <a href="https://stackoverflow.com/questions/48288558/reading-data-from-serial-bus" rel="ugc">https://stackoverflow.com/questions/48288558/reading-data-from-serial-bus</a> The COM port communication has not changed since it was invented, has nothing especially to do with USB as this is mapped to a "normal" (software) COM port. So the knowledge about that is the same as for old modems or acoustic couplers... Cheers, Christian
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Communication accross Serial Ports (aka COM) ports needs: First establish the standard: RS232, RS423, &nbsp; most probably: RS-232 Then establish the protcol being used... &nbsp;3 wire, (ground, send, receive) 5-8 wires (send, receive, basic modem control) &nbsp;or more wires (full modem control). Then establish the signals used for sync: hardware (RTS, CTS, ..) or software: XON/XOFF... (Obviously they both need to adhere to the same speed, &amp; framing (BaudRate, bits/frame, start, stopbits (1, 1.5, or 2 )).) XON/XOFF (CTRL/Q &amp; CTRL/S) are characters send down the line stop/start transmission this is about buffer management. Both sides need to use the same protocol to allow successful transfer of data. You cannot handle XON/XOFF in a high level program, that needs to be done on the driver level same for CTS/RTS hardware signals. So you need to setup the serial port drivers to honour the required protocols. Most often the peripheral equipment dictates the settings you need to setup in a computer. Also most often settings can be either set during an openstatement , or using some IOControl command after opening a channel. Handy tools to use are classic terminal emulators that ALSO understand serial port communication (putty (the extended one) , minicom, kermit, etc.)
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Managing Patner

Hankwembo Christopher,FCCA,FZICA,CIA,MAAT,B.A.Sc

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Many thanks to the following professionals on this forum: <a href="https://www.experts-exchange.com/members/JDettman.html" rel="ugc">Jim Dettman (EE MVE)</a>&nbsp; The point you have highlighted above to be more specific sir: &nbsp;1. A large buffer for sending and one for receiving data.&nbsp; Thanks a million you have finally put this endless issue to a permanent end for good,without this hint I just busy hunting for answers in a wrong place altogether.Below are the main issues which were hidden: (1) The Modbas I'm using was done somewhere in 1999, from what I have seen after analysis, it became very clear that this Modbas has only the send &amp; receiving buffers of 1K each and was only able to hold data with a length of 1042. (2) Since I did not know the length of the data in the gadget, I kept on increasing the buffers gently until I reached 12k per buffer, at this point when I offloaded the output in the note pad I was able to see now all the data including the CRC. (3) The total length of that data was 8309 , can you imagine, the data I needed had only a length of 1020 meaning the difference was just unwanted data which was essentially remaining in the gadget and eventually chocks Ms Access. &nbsp; (4) Final discovery the Modbas I'm using was actually designed to handle measuring scales with small buffer of less than 1K Bill Prew Many thanks to you a million for helping previously the more technical areas of the gadget I'm using: (1) Interpreting the technical guide, frankly I was completely lost on this (2) Converting CRC which was written in C++ into VBA (3) Constructing the correct data packet (header1,header2,CommandID,Length in Big endian,Actual data(Json) &amp; CRC) and balancing (4) Cleaning up the codes Many thanks once again to you all. Regards Chris
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Chris, &nbsp; Even with larger buffers, you may not be done yet. &nbsp; &nbsp;You may find a buffer large enough that always works, but really you should be implementing flow control. &nbsp; Say you are receiving and you have a 12K buffer, but are still processing what has been received. &nbsp; Your buffer stands at 80% full. &nbsp; What needs to happen is you need to tell the sending side to stop sending until you catch up. &nbsp; Once you have, then you can tell it to start again. &nbsp;When you do this, you can work with any size buffer. &nbsp;This is inherent in serial communications. &nbsp; There are two types; out of band and in band. &nbsp; Out of band is done at the hardware level outside of the data.using the RTS/CTS signals (Request to Send / Clear to Send). &nbsp; In band is done within the data and uses X-ON/X-OFF characters or some other escape character. &nbsp;At this point, you may not want to get into this, but I think you should.&nbsp; &nbsp;If for example all of a sudden you get twenty invoices worth of data, your current buffer may not be large enough. Jim.
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After working throughout last night on the serial USB Port to find out exactly what was causing Ms Access to hang/restart before finishing the second invoice,I discovered fortunately the main issue,Firstly, I had to use the note pad to divert the actual data that was coming out from the gadget to analysis it line by line including the commas &amp;&nbsp;other characters and the results after comparing it with the gadget manual provided turned out as below: 
 
(1) The QR code details were missing or not coming out of the gadget 
(2) The CRC was also missing 
(3) The closing Braces &amp;&nbsp;Square brackets were also missing 
 
 
Conclusion only 90% of the data were being extracted from the port leaving 10% inside, that is why Ms Access had a problem of hanging/restarting. 
 
Help required 
 
Extra VBA code to loop through the CommRead Function to force all the data to come out of the serial port before process any data and writing to the table. I'm trying the code below but it appears I'm missing it somewhere: 
 
 
CommRead Function 
 

<pre><code class="code-10 nolinks" id="code-10-29188028-1">' Read maximum of 2034 bytes from serial port.
 lngStatus = CommRead(intPortID, strData, 2036)
 'Do loop
 Do While lngStatus &gt; 0
 
 If lngStatus &lt; 0 Then
 Exit Do
 
 Set json = JsonConverter.ParseJson(Chr(91) &amp; Mid(strData, 8) &amp; Chr(34) &amp; &quot;}&quot; &amp; Chr(93))
 
 On Error Resume Next
 
 End If
 Loop
</code></pre>
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After working throughout last night on the serial USB Port to find out exactly what was causing Ms Access to hang/restart before finishing the second invoice,I discovered fortunately the main issue,Firstly, I had to use the note pad to divert the actual data that was coming out from the gadget to analysis it line by line including the commas & other characters and the results after comparing it with the gadget manual provided turned out as below:

(1) The QR code details were missing or not coming out of the gadget
(2) The CRC was also missing
(3) The closing Braces & Square brackets were also missing


Conclusion only 90% of the data were being extracted from the port leaving 10% inside, that is why Ms Access had a problem of hanging/restarting.

Help required

Extra VBA code to loop through the CommRead Function to force all the data to come out of the serial port before process any data and writing to the table. I'm trying the code below but it appears I'm missing it somewhere:


CommRead Function

(CODE)

How to use Loop in the serial port programming

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