afx wrote:The problem is that I had to put a "Thread.Sleep" (between 5 and 20 ms) inside loop that transfers the individual bytes in PC side so the connection is reliable.
The Q68 SER has no hardware handshake, so you need to be sure the receiving software actually processes its input fast enough. For typical usage like COPY or SERNET this was tested from PC to Q68, and should be no problem. But I don't know about your BASIC program.
What kind of serial port do you have on PC side?
Remark: I'm a little surprised, how widely the SER port is used on the Q68. Wish there had been two more pins on the FPGA for hardware handshake.