N°98.60.17.013.0
14/ 19
080424/1
Sentinel unit transmits “Infinite” value to indicate an overflow measure and “NaN” value to
indicate a too inaccurate measure such as impedance measurement when the temperature or
the voltage is too high or new impedance measurement in a delay time shorter than 10
minutes from the previous one.
On MEASURE command, the Sentinel unit doesn’t acknowledge this command.
On TRANSMIT command, the unit transmits the last specified measurement from storage,
which is indefinitely retained until new measurement of same parameter.
On MEASURE & TRANSMIT command, the Sentinel unit performs the measurement then
transmits that measured value
When response just includes status information for the controller and not measurement
values, data format is always 2 bytes, with general flag, MSB bit 7 in first byte, SET and any
unused bit cleared to 0. Examples of such response:
- SEND ID : 0xA0, 0x00
A prompt to the controlling device’s ASSIGN ID command. Indicates that the unit requires the
new ID to be sent.
- ID CHANGED: 0xC0, 0xID
A response to the controlling device’s compliance in sending the new ID. The new ID must be
included in the response. Specifically, the ID does not change from old to new until this
response has been sent.
- TRANSMIT twice: 0x90, 0x00
If the unit determines that it has received two successive TRANSMIT commands (for the same
measurement type), it doesn’t return the same value but a status (0x90 0x00) that indicates to
the controlling device that this has occurred, with flag set.
- “READY” announcement : 0x80, 0xSW
Following a successful start-up, the unit issues a “READY” announcement. Take care that at
this moment,
the system controller must be in listener only mode
. This is the only
unsolicited transmission to the bus that the unit is allowed to make, and subject to conditions.
Its purpose is :
a) to serve as a confirmation message to the OCS that the unit
has
reset, and
b) during the system installation phase, to signal to the OCS the presence of a new Unit on
the bus.
Parameter
Data A, Data B Flag, Exp, Mant
Value
Voltage
0x55, 0xA0
0 1010 10110100000
13.625 V
Voltage
0x41, 0x00
0 1000 00100000000
2.25 V
Temperature 0x69, 0xD0
0 1101 00111010000
78.5 °F
Impedance
0x3C, 0x80
0 0111 10010000000
1.5625 mO
