UM0934 datasheet(95/113 Pages) STMICROELECTRONICS

95 / 113 page

UM0934

Extended functions

Doc ID 17389 Rev 2

95/113

Both NTX and NREJ values are programmable by accessing the MIB object 0085h

(Section 6.5.27). Default values are NTX = 8 and NREJ = 9.

Figure 23

shows the transmission of an alarm with default values.

Figure 23.

Alarm transmission

7.2.2

Alarm reception

As soon as a burst of alarms is received, the ST7570 generates a CMD_AlarmIndication

message to the host.

In order to avoid the detection of fake or corrupted alarm messages, the system generates

an indication only if NRX consecutive alarms are received. Parameter NRX is programmable

through the MIB object 0085h (Section 6.5.27).

After the CMD_AlarmIndication message, the ST7570 ignores all the alarms that may occur

in the next NREJ time-slots.

If a CMD_AlarmRequest message is sent during the alarm reception or the reject window,

the ST7570 provides an immediate positive confirmation but it does not transmit any

additional alarms.

Default values are NRX = 2 and NREJ = 9.

Figure 24

shows the behavior of a node (node 2) with NRX = 2, assuming that node 1 is

transmitting an alarm burst (with NTX = 8 and NREJ = 9).

Alarm

Request

Alarm Transmission (N

TX )

Reject Window (N

RE J)

Alarm

Confirm

Alarm RECEPTION

Alarm IGNORED

Alarm TRANSMISSION

UM0934 Datasheet(PDF) 95 Page - STMicroelectronics