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Commands
Group 2 and 3: FIFO Input Register and FIFO Monitor Input Register
Breakdown of the Areas in the Input Register
FIFO memory
The input data of each channel is stored in two FIFO memories with identical structures. Each
FIFO memory is composed of 32 elements.
The utilization of a FIFO memory is indicated in the first register of the relevant channel. When
registers are read from the memory, the channel content in the memory is shifted along one
memory element. A master can therefore read data from the memory only once.
A protocolling master addresses the device using device ID 2. The protocolling master only has
read permissions for the third group.
Utilization of the FIFO Memory
Utilization indicates the percentage of the FIFO memory occupied by data that has not been
retrieved. If the response data of the device is retrieved at a lower rate than new data is
generated, the FIFO memory overflows and data is lost. In order to avoid data loss, ensure that
utilization remains below 15% by setting a high polling rate.
7.7.3
MODBUS commands
The IDENTControl Compact supports the MODBUS commands
read holding registers
,
write multiple registers
and
read/write multiple registers
.
The MODBUS master issues a command by sending a request. The slave (IDENTControl
Compact) sends a response that corresponds to the MODBUS specifications. If an error
occurs, the response contains an exception code.
Command: write multiple registers (10h)
This MODBUS command (request) starts system commands and read/write commands. You
must know the following parameters to make the request:
Address
(0-based,
decimal)
Byte number of the
identification telegram
Use
0 + K
-
Reserved
-
Utilization A
1 + K
Byte 0
Telegram length, high byte [(N+1) div 256]
Byte 1
Telegram length, low byte [(N+1) mod 256]
2 + K
Byte 2
Command code (Echo)
Byte 3
Reserved/channel/toggle bit
3 + K
Byte 4
Status
Byte 5
Reply counter
I + K
Byte N-1
Data
Byte N
Data
Table 7.5
K = 0, 1000, 2000, 3000, 4000
I = 4, 5, 6 etc.
Utilization Meaning
0
No data available
1
–
100
Data available
101
Data available, but data lost due to FIFO memory overflowing
