DekTec DTM-3200 IP-ASI Converter - Manual (Page 20)

DTM-3200 – OEM Ethernet TSoIP Converter
User Manual
20
Figure 6 below shows the structure of a command written through the serial interface. 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 6. Command on an RS-XXX serial control interface
All commands successfully sent to the DTM-3200 are answered with a copy of the command
including the data bytes.
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 with the ASCII character ‘E’ and the data is removed from the message.
4.2.2 Command protocol on I 2 C
Field Format Description
Start S Standard I 2 C start condition
Address I 2 C address byte 7-bit I 2 C address followed by the I 2 C R/W bit, which is set to
0 and 1 in the command- and response sequence
respectively
Category 1 byte Selects a “category” of settings
Setting 1 byte Selects a setting within the selected category
Read/Write 1 byte 0x01 for read and 0x00 for write
Index 2 bytes (Optional) Provides an extra index parameter, e.g. to
indicate the channel number 6
Data n bytes The data written or read. The data length is variable for
each setting. In case of a write operation, the actual data is
returned as a (negative) acknowledgement
Checksum 1 byte This is the least significant byte of the two's complement of
the sum of the 7-bit I2C slave address and all data-bytes in
the I2C message (excluding the checksum). The I2C R/W bit
is not included, an incorrect value of this bit would cause the
checksum to be not received at all.
End P Standard I 2 C stop condition. A repeated start condition can
be used at all times to concatenate multiple I 2 C read / write
actions
6 The DTM-3200 supports a single channel only. Whenever index is used as a channel number, it shall/will be set to 0.