2 command protocol on i2c, 2 command protocol on i – DekTec DTM-3237 DVB-S2 Receiver User Manual
Page 16

DTM-3237 – OEM DVB-S2 Receiver with DVB-ASI Output
User Manual
16
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
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
Figure 3 below shows the sequence to send a command over I
2
C to the DTM-3237. In the examples
below, grey areas in the timing diagrams are sent by the DTM-3237, while white areas are sent by
the I
2
C master. If the command is a read-command, the data may be omitted. Note that some
settings require an index.
Figure 3. Command (upper sequence) and response (lower) sequence for I
2
C
6
The DTM-3237 supports a single channel only, so when index is used as a channel number, it’s always 0.