APM3.2.1固件-VS2012工程

JETI Telemetry communication protocol

This document describes a telemetry communication protocol that is used by sensors of JETI model. Telemetry

information is transmitted through a one-wire bus from sensors to receiver. As a following step, the information is

wirelessly sent to another device, such as transmitter, TX module or JETIBOX profi.

Topology

The bus has a topology called “point to point”. Every sensor is marked as a “master” because it always initiates

communication. A device connected to the sensor is marked as a “slave”. If several sensors are connected, it is

mandatory to use a multiplexer (Expander), that processes all inputs and transforms them into one single output.

Communication lines RX and TX are physically connected through a resistor with resistance of a few kilo-ohms

(see the following picture).

RX

TX

uP

k

Ω

COM

Logic levels:

Maximum level of logical zero “0”: 1,5V

Expander

Receiver or

JETIBOX

Master

JETI Telemetry communication protocol

After transmission, the bus is released in the following way. The TX line is reconfigured as an input with use of an

additional internal pull-up resistor. After timeout has passed, the TX line returns into output state. “Slave”

(JETIBOX) sends information about buttons pressed within specified time.

Network protocols

Currently there are four protocols existing. Protocol of the lowest layer is called “simple text” and is included in

every communication packet. The rest of protocols are parts of a higher layer. During a procedure of packet

Expander

JETI Telemetry communication protocol

Protocol of alarms

Alarm message informs about exceeding maximum/minimum values set in the devices. Protocol includes a letter

encoded in Morse Code alphabet, which is later acoustically signalized.

The EX protocol exists in two forms – text and data protocol. Data specification is dedicated to transmitting

sensors' values directly in a binary form. Text specification provides human-understandable labels to data

specification.

For example a temperature sensor, SENSOR T:

Data packet transmits information about temperature measured on input 1 and input 2. Text packets describe

For third party devices you are free to use the upper part of a serial number within range 0xA400 – 0xA41F.

The lower part of a serial number should be used in a manner it ensures uniqueness of the whole serial number

(4B). Maximum allowed length of a packet is 29B (together with separators 0x7E; 0xNF).