Commands
2014-
02
33
Groups 2 and 3: FIFO input register and FIFO monitor input register
Each area of these groups is divided as follows:
K = 0, 1000, 2000, 3000, 4000
I = 4, 5, 6...
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 the response data is
generated, the FIFO memory overflows, which results in a loss of data. Therefore, make sure
that a sufficiently high polling rate is set to ensure that the utilization value remains as far below
15 % as possible.
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.
7.3.3
Supported MODBUS commands
write multiple registers (10h)
This MODBUS command (request) is used to start system commands and read/write
commands. The device sends a response to a
write multiple registers
command as outlined
in the MODBUS specification. In the event of a fault, a corresponding response is issued with
an exception code.
Process:
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 7.3
FIFO input register and FIFO monitor input register
Utilization value
Meaning
0
No data available
1 .. 100
Data available
101
Data available, but data lost due to FIFO overflow
Table 7.4
Utilization value and occupancy of the FIFO memory in percent
