TDataPacket and TComPort wait until receiving packet

Question

i'm working on ecr software.

This software talks with hardware that has com port.

I'm programming in delphi and i'm using TComPort and TDataPacket component.

I have a problem (i think, or maybe i don't understand how tdatapacket works).

For printing a receipt i have to send to the hardware some string formatted by protocol rules.

The protocolo for printing is this:

Me: ENQ

HW: ACK

Me: STX + string + checksum(string) + ETX

HW: ACK

Me: STX + string + checksum(string) + ETX (closing string)

HW: ACK and print the receipt

I wrote this code:

procedure TForm1.Button4Click(Sender: TObject);
var
  snd, ckSum: String;
  checkSum : Byte;
begin
  if ack = #$06 then
  begin
    snd := '5/1/0.00//1.000000/SALDO/';
    checkSum := calcCheckSum(snd);
    ckSum := formatfloat('00',checkSum);
    ComPort.WriteStr(#$02 + snd + ckSum + #$03);
  end;
end;

and on the datapacket on packet event this:

procedure TForm1.ComDataPacket1Packet(Sender: TObject; const Str: string);
begin
  ack := Str;
end;

But if i try to print the value of ack i always have empty string, what i'm doing wrong?

Answer 1

Try using ComPort.Read and get the readed data buffer, after you can parse it according at all that you need.