Read Weight from Weighing Indicator Sang D500svia RS232

Hi all.
Hope you all well.

I'm trying to create an application which read weight from Sang Weighing indicator.

My application works fine on Mettler Toledo Ind-221 but when i link my serial port with Sang D500s Weighing indicator nothing happens data is not retrieved.

Data is shown on hyper terminal.

Can anyone please help me out.

This is my code.

comPort.Open()
comPort.Write(STX)
comPort.Write("P")
comPort.Write(CR)
str1 = comPort.ReadExisting

It works on Mettler toledo but not on Sang.

if i remove all the code and write str1 = comPort.ReadExisting
my code stucks.

Regards
Saad Khatib