B&B Electronics ZZ24D-NA(NB,NC,ND)-SR - Manual - Manual (Page 57)

Configuration & Operation
Manual Documentation Number: pn7515_ZlinxIO-0712m 51
Analog Exception errors are generated when user-defined High or Low limits are exceeded. If an Analog Input value rises
above the High limit, an exception is generated and immediately sent out. Data is updated and retransmitted based on the
Exception Retransmit timer. Exception is transmitted in the timeframe predefined by the user within the allowable range. If the
Exception reporting timeout is set to zero, the exception is sent only once to the Modbus Master.
 Analog Value > HIGH LIMIT = Exception Error.
The High exception error is cleared when the Analog Input value falls below the high limit – the dead band value.
 Analog Value < (HIGH LIMIT – DEAD BAND) = Exception Error Cleared.
If an Analog Input value falls below the LOW limit, an exception is generated and immediately sent out. Data is updated and
retransmitted based on the Exception Retransmit timer.
 Analog Value < LOW = Exception Error.
The Low exception error is cleared when the Analog Input value rises above the low limit + the dead band value.
 Analog Value > (Low + DEAD BAND) = Exception Error Cleared.
5.1.5.1 Sample Modbus Exception Packet
Exception Modbus packets do not follow the typical Modbus protocol. The Base Module is a Slave device and in a typical
system, slave devices do not generate outgoing requests. When the Base or the exception Expansion Module (1st module
next to the Base Module) generates an exception, the Base Module will generate a Modbus packet that emulates a “Master
Poll”. The exception packet is sent to the Master and does not require an ACK.
5.1.5.2 Digital Exception Format
Base Module DI exception
01 02 00 01 0E 98 2C
Exp Module DI Exception
01 02 10 01 CE 99 B9
01 Slave Address
02 Function (Read DI’s)
00 I/O Address High (0-15 = Base, 16-31=EXP module 1)
01 Byte Count
0E Digital Inputs (8-DI’s) 1110
98 Checksum High
2C Checksum Low
5.1.5.3 Analog Exception Format
Base Module AI exception
01 04 00 08 00 00 00 00 00 00 00 00 98 2C
Exp Module AI Exception
01 04 10 08 00 00 00 00 00 00 00 00 99 B9
01 Slave Address
04 Function (Read AI’s)
00 I/O Address High (0-15 = Base, 16-31=EXP module 1)
08 Byte Count 08
00 Analog Input-1 High Byte
00 Analog Input-1 Low Byte
00 Analog Input-2 High Byte
00 Analog Input-2 Low Byte
00 Analog Input-3 High Byte
00 Analog Input-3 Low Byte
00 Analog Input-4 High Byte
00 Analog Input-4 Low Byte
98 Checksum High
2C Checksum Low