Garmin Apollo SL40 Installation Manual

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Serial Data SpecificationsApollo SL40 Installation Manual 27APPENDIX E - S ERIAL INTERFACE S PECIFICATIONSThis appendix includes the interface specifications for the RS-232 serial port. The RS-232port can be used to input active and standby frequencies, and is used to input frequencies froma remote source, such as the SL50 and 2001GPS. The interface format conforms to NMEA0183 message format specifications.The format of the RS-232 serial port is as follows:Baud rate............................................ 9600Data bits............................................. 8Stop bits............................................. 1Parity.................................................. noneThe data format is as follows:$PMRRCThe checksum is computed by an 8 bit addition of the msg_id and msg_data characters,ignoring carry if any. The resulting 8 bit checksum is converted to two ascii characters bytaking the upper and lower nibbles, adding 30h to each, and placing the most significantcharacter first in the data message.RS-232 I NPUTSSET ACTIVE FREQUENCYMessage Format$PMRRC00mka00 ....... message idmk...... active frequency:m = desired frequency in MHz in hexadecimal, where m = desired frequency -30h , with desired frequency in range of 118 to 136 MHz, or 162 MHz.k = desired frequency in kHz where k = (desired frequency / 25 kHz) + 30h, withdesired frequency in range of 000 to 975 kHz in 25 kHz steps, or 0 to 39.a ......... transceiver function:N = normal receive operationM = enable monitor function0 = no changeExample Message$PMRRC00G4N29Set the active frequency to 119.100MHz, normal receive mode. “G” = 119d - 30h = 77h -30h = 47h, or an ascii “G”; “4” = 100 kHz/25 kHz + 30h = 4 + 30h = 34h, or an ascii “4.”