Garmin SL40 - Manual (Page 33)

Serial Data Specifications
Apollo SL40 Installation Manual 27
A
PPENDIX
E - S
ERIAL
I
NTERFACE
S
PECIFICATIONS
This appendix includes the interface specifications for the RS-232 serial port. The RS-232
port can be used to input active and standby frequencies, and is used to input frequencies from
a remote source, such as the SL50 and 2001GPS. The interface format conforms to NMEA
0183 message format specifications.
The format of the RS-232 serial port is as follows:
Baud rate............................................ 9600
Data bits............................................. 8
Stop bits............................................. 1
Parity.................................................. none
The data format is as follows:
$PMRRC
The 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 by
taking the upper and lower nibbles, adding 30h to each, and placing the most significant
character first in the data message.
RS-232 I
NPUTS
S
ET
A
CTIVE
F
REQUENCY
Message Format
$PMRRC00mka
00 ....... message id
mk...... 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, with
desired frequency in range of 000 to 975 kHz in 25 kHz steps, or 0 to 39.
a ......... transceiver function:
N = normal receive operation
M = enable monitor function
0 = no change
Example Message
$PMRRC00G4N29
Set 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.”