The electronic VSI generally has much less drift compared to a mechanical VSI and this function
will only be used very occasionally. Ensure that you perform this function when no pressure
changes due to wind or other reasons are occuring.
It is normal for the VSI to show short, small positive or negative readings when your aircraft is
standing still on the ground. The digital VSI is very sensitive and will show very small changes in
pressure.
SP …
Select the protocol you would like to use for the serial output. Please see the following protocol
section for available protocols and their exact definition. You must select the correct protocol for
the device connected. Note that only the ALT-5 supports serial protocols.
IIMorrow serial protocol
The IIMorrow protocol uses RS232, 1200 baud, 8 data bits, one stop bit, no parity.
Message transmission rate is once per second.
Example altitude message for 10500 ft:
#AL +25D7cr
The message consists of #AL followed by a space.
This is followed by a “+”, then five digits for the altitude in feet relative to 1013mB local pressure
setting. The altitude is padded with leading zeros if required to make up five digits.
This is followed by the letter “T” , a “+”, the two digits “25” and a single byte checksum over all the
characters in the message up to and excluding the checksum. The checksum is a simple modulo
256 sum of the binary values of the individual characters. The checksum is sent as two
characters in hexadecimal format. The message ends with a carriage return (0x13).
Negative altitudes are transmitted as 00000. Altitudes are transmitted in feet.
Trimble/Garmin protocol
The Trimble/Garmin protocol uses RS232, 9600 baud, 8 data bits, one stop bit, no parity.
Message transmission rate is once per second.
Example altitude message for 10500 ft:
ALT 10500cr
The message consists of the three letter “ALT” followed by a space. This is followed by a five digit
altitude relative to a local pressure setting of 1013mB. The altitude is padded with leading zeroes
if required to make up five digits. Finally the message is terminated with a carriage return (0x13).
Negative altitudes are transmitted as 00000. Altitudes are transmitted in feet.
MGL protocol
The MGL protocol uses RS232, 9600 baud, 8 data bits, one stop bit, no parity.
Message transmission rate is once per second.
Example altitude message for 10500 ft:
Summary of Contents for Stratomaster Maxi Single ALT-3
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