Sailor RM2042 Technical Manual page 59

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