I have a first MCV300 CNC and am using an iLogic DNC and it keeps oveflow alarming after a while during each program. I have changed the DNC to feed by character instead of line and it works but it makes the machine 5x slower. I am using a good usb to serial cable and nothing seems to change. Any suggestions?
1. the PC's Serial Port does not react quickly enough, when using software handshaking, to an Xoff (DC3 - Ascii 19) character,
2. the control is not set to use DC1 to DC4 characters, and accordingly, is not transmitting an Xoff control character. You didn't mention the model control you're using, but most Fanuc control models can be explicitly set, or not, to use these characters.
For 1 above, if Xon Xoff (software handshaking) is being used, the problem can frequently be remedied by adjusting the FIFO settings of the Serial Port being used. This is accessible via Device Manager > Ports (Com & LPT) > (Select the port being used) > Port Settings > Advanced.
For 2 above, make sure that the Input/Output device is set via parameter to RS–232 (Used control codes DC1 to DC4), if your Comms software is set to use Xon Xoff handshaking.
If software handshaking is being used, with the correct Input/Output device set at the control, and the fix in 1 above does not help, you can use Hardware (RTS/CTS) handshaking. This is always more reliable, as handshaking is achieved by toggling the voltage on the handshake lines to +3VCD and above for logic 1, and -3VDC and below for logic 0. Between +3VDC and -3VDC is used to accommodate noise. The voltage on these lines will depend on the power supply being used by the device, and can be between +24VDC to -24VDC, but usually around +- 10 to 15VDC. To use hardware handshaking, you need a cable pin out that uses the hardware handshake lines.
If you're unsure of the parameters to set at the control, post the model control being used and I, or another Forum member will advise you on that, and the cable pin out. Also, post the operating system being used with your lap top (I assume lap top because of the USB to Serial adapter).