Installation manual

Serial Interface Specifications

56 Apollo SL30 Installation Manual

DATA FORMAT

The data format for the serial communication is:

• Baud rate 9600

• Data bits 8

• Stop bits 1

• Parity none

MESSAGE FORMATS

All messages will conform to the NMEA 0183 proprietary message format as follows. All

characters will be standard ASCII characters. No binary data characters will be used.

“$” .......................... Start of message character, ASCII “$” (024h).

“P” ........................... Proprietary message identifier.

“MRR” .................... II Morrow company identifier.

c................................ Message class identifier. Used to identify a message as either a

COMM or a VHF NAV message. Those message types which are

also supported by the SL40 VHF Comm Radio Serial Interface will

use the “C” identifier to allow the SL30 to accept COMM radio

commands from existing products. All other messages will use the

“V” identifier to indicate that they relate to a VHF NAV receiver.

nn ............................ Message identifier, two-digit number in ASCII characters.

d.....d ...................... Message data characters defined for each message.

chksum .................... Message checksum, including message identifier through data

characters. The two-digit checksum is generated by adding all

values of valid characters together, ignoring carry (if any). This

value is converted into two encoded hex

characters (30h-3Fh).

<CR> ...................... ASCII carriage return (0Dh).

<LF> ....................... ASCII line feed (0Ah).

The maximum message length, including the start of message character (“$”) and the end of

message <CR><LF> sequence, is 25 bytes.

This message format is the same as is used in the SL40 VHF Comm Radio. The SL30 will be able

to accept all messages intended for an SL40 without generating a serial communications error. It

will ignore all of those messages, the only exception being those messages used to input Comm

frequency lists from a remote source.

Encoded hex: each character consists of 4 bits of data placed in the low order nibble +30h. For example, the 8-bit

value 5Fh would be encoded as two characters with values of 35h and 3Fh, which map to the ASCII characters “5”

and “?”, respectively.