ptp via cp340 using 3964R

[Guest pol]

Hi, I made a ptp-connection between two S7-300 stations on a leased line using 3964® protocol. Both stations have one or more CP340 (rs232). Line transport is at 2400bps via westermo TD32 modems. Receiving 11 bytes of data using FB2 and sending 3bytes with FB3, sending starts when FB2 returns NDR-signal (end without errors), FB2 is allways enabled. Complete program is in OB1, cycle time is very short (1 or 2 ms) This setup worked fine for months. Since a week or so, the connection stops after a few hours, the only way to get started again is by going into stop and start again. Diagnostic buffer of CP340 gives fault-code 080A : no free receive buffer is available. What could be the reason of this error and is there a way of clearing the receive buffer in the program? Pol