Hi,All My hardware requires RTS signal from PC COMx port be OFF state(negative voltage, about -9V), but Keil C51 debugger Monitor51 always turns on RTS signal(positive voltage, about +9V).Keil new ISD51 seems provide flexibility to select RTS be one of four states: high, low, active high, active low. If possible, actually I'd prefer RTS be active high. does anybody know any means to control RTS in debugger Monitor51? Thanks a lot.