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

Page 16

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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.