data bits. The data bits are transferred starting with the LSB and proceeding in order to the MSB or parity bit. A stop bit is a “1” that is sent after the data bits to indicate the end of the transmission. This “1” resets the signal to the idle state so it is ready to wait or transfer more data. For example, if we wanted to represent the ASCII character ‘A’ it would normally be represented by the binary number 01000001. If we wanted to transfer this letter ‘A’ across and asynchronous serial transmission system we would have to include the start and stop bits and the new representation would be 0010000011.7.An interrupt function allows the assembly programmer to call up an operating system subroutine. This function is denoted by the command INT. The 14 in the command INT14H refers to the interrupt that will initialize the asynchronous communications port and return the status of that port.DB-25 pin assignments PinNameSignalPinNameSignal1FGFrame ground14STDSecondary TD2TDTransmitted data15TCTransmit clock3RDReceived data16SRDSecondary RD4RTSRequest to send17RCReceive clock5CTSClear to send18-Unassigned6DSRData set ready19SRTSSecondary RTS7SGSignal ground20DTRData terminal ready8DCDData carrier signal21SQSignal quality detector9-Positive voltage22RIRing indicator10-Negative voltage23DRSData rate selector11-Unassigned24SCTEClock transmit external12SDCDSecondary DCD25BUSYBusy13SCTSSecondary CTS...
