DekTec DTM-3200 IP-ASI Converter - Manual (Page 21)

DTM-3200 – OEM Ethernet TSoIP Converter
User Manual
21
Figure 7 below shows the sequence to send a command over I 2 C to the DTM-3200. If the command
is a read-command, the data may be omitted. If the category does not require an index, the index
must be omitted.
Figure 7. Command (upper sequence) and response (lower) sequence for I 2 C
When an incorrect checksum is detected, the DTM-3200 will not return an answer. When protocol-
errors are detected, e.g. a combination of a valid category with an invalid setting, the R/W byte of
the reply is replaced by the ASCII character ‘E’ and the data is removed from the message.
When a master starts writing to a device while the previous command is still being executed, this
device replies with a NACK.
When a master starts reading from a device and there is no answer available (yet), the device will
reply with the value 0x00. The value 0x00 will be returned until an answer is available and the
master has initiated a new read transaction.
Note: In DTM-3200 package versions v1.3 and lower, in the case mentioned above, the device
replies with a NACK instead of the value 0x00.
S and P are the standard I
2 C start and stop conditions. A repeated start condition can be used at all
times to concatenate multiple I 2 C read / write actions.
4.3 Manageable items
The tables in this section provide lists of variables that can be configured and/or monitored using
the I 2 C or RS-232/485/422 interface. The ‘Access’ column indicates whether the variable is Read
Only (RO), Write Only (WO), Read/Write (R/W) or not applicable (n.a.).
When, in the 'Access' column, the text "(V)" is written after the access type, the variable can be stored
either in a volatile or non-volatile manner, depending on the 'Volatile Storage' setting (category
0x02, setting 0x03). The volatility of the variables without "(V)" cannot be controlled.