TECHNICAL MANUAL FOR COMPACT VHF DSC RM2042

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS RM2042The received serial data is stripped for start, parity and stopbits and converted to parallel data. When aparallel databyte is ready, the UART uses RXRDY to interrupt the microprocessor, which fetches the bytefor further processing.The UART is a full duplex device, but the interface is constructed with a single line by means of Q6 andU2.1, using half duplex communication. In order to avoid conflict on the line, a master/slave relationshipis established. RM2042 is the master and has control over the line. If the VHF wants to use the line itinterrupts RM2042 via pin 7 in P2.The signal levels are 0 and 5V DC.PRINTER INTERFACEThe printer interface is a Centronics compatible parallel interface implemented by the port IC U10.The microprocessor writes parallel data to port A. When data is accepted by the port IC, pin PC7 goeslow, and the printer strobe generator circuit on the microprocessor module, generates a 2 s delayed, and4 s wide logical low strobe. The printer answers by setting the busy flag high (input to PC0). When theprinter has processed the data, the busy flag is removed (now logical low), and the printer generates alogical low acknowledge pulse which is input to pin PC6. PC7 changes to logical high, and the port IC isready to write another byte to the printer. If PC6 is kept low, data written to port A is lost, because outputon PC7 is inhibited and no strobe is generated.C2149/PC INTERFACEThe C2149/PC interface is a standard RS232C interface implemented with the UART U8 and the RS232line driver/line receiver U11. U11 generates the RS232 signal levels of +/-9V from the single 5V supply.The UART handles the transmission and reception of serial data. The transmission rate is 4800, E, 8, 1.During transmission, the UART uses TXRDY to interrupt the microprocessor when it is ready to transmitanother byte. During reception, the UART uses RXRDY to interrupt the microprocessor and tell that a bytehas been received.If a C2149 remote box is connected, it can receive its supply voltage via pin 6 in J3.NMEA 0183 INTERFACENMEA0183 is the international standard for interfacing marine electronics navigational devices.NMEA0183 provides for asyncronus transmission, with a single talker and multiple listeners per line. Thestandard uses an 8 bit ASCII, parity disabled, block oriented protocol with a transmission rate of 4800baud.The incoming signal is electrically isolated from RM2042, by the optocoupler OC1. Because of the signaldeformation in the optocoupler, the signal is sent trough the Schmitt-trigger build round U2.4. The serialdata is received by the UART U7. The UART uses RXRDY to interrupt the microprocessor whenever abyte is received.9341PAGE 5-3