[Micro830: ARD function can not receive data]

hello, i'm using Micro830 to receive serial data from matlab and hyperterminal. i followed article 448488 - how to read ASCII in Micro800 controller. However, ACB can receive data but ARD can not.  
Then i added a contact before ARD. Once i check and recheck it, then ARD can receive data and ACB value will be cleaned.

the 55 showed on the ARD is the value from previous buffer

 

[Serial communication of Micro830]

hello everyone, I'm trying to connect PC with Micro830 with RS232 cable for transfer serial data. However, the PLC can not receive the character from PC.

1. I used ARD function block to read the characters from PC. 
2. there is no error and the output of ARD function block is 0 when I debug ladder programme.
3. the serial communication state LED illuminated once I send a character from PC to PLC.
4. the channel of input is 2 which is the embedded serial port.
5. I use an adapter from USB to RS232.

Email: jeremietang531@gmail.com