DS125BR800 Datasheet, PDF (23/59 Pages) Texas Instruments – Low-Power 12.5-Gbps 8-Channel Repeater With Input Equalization and Output De-Emphasis

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DS125BR800
SNLS426E – AUGUST 2012 – REVISED JANUARY 2015
STOP: A Low-to-High transition on SDA while SCL is High indicates a message STOP condition.
IDLE: If SCL and SDA are both High for a time exceeding t_BUF from the last detected STOP condition or if they
are High for a total exceeding the maximum specification for t_HIGH then the bus will transfer to the IDLE state.
8.5.3 System Management Bus (SMBus) and Configuration Registers
The System Management Bus interface is compatible to SMBus 2.0 physical layer specification. ENSMB = 1 kΩ
to VDD to enable SMBus slave mode and allow access to the configuration registers.
The DS125BR800 has the AD[3:0] inputs in SMBus mode. These pins are the user set SMBUS slave address
inputs. The AD[3:0] pins have internal pull-down. When left floating or pulled low the AD[3:0] = 0000'b, the device
default address byte is 0xB0. Based on the SMBus 2.0 specification, the DS125BR800 has a 7-bit slave address.
The LSB is set to 0'b (for a WRITE). The device supports up to 16 address byte, which can be set with the
AD[3:0] inputs. Table 9 shows the 16 addresses.
Table 9. Device Slave Address Bytes
AD[3:0] Settings
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Address Bytes (HEX)
B0
B2
B4
B6
B8
BA
BC
BE
C0
C2
C4
C6
C8
CA
CC
CE
The SDA, SCL pins are 3.3 V tolerant, but are not 5 V tolerant. External pull-up resistor is required on the SDA.
The resistor value can be from 1 kΩ to 5 kΩ depending on the voltage, loading and speed. The SCL may also
require an external pull-up resistor and it depends on the Host that drives the bus.
8.5.4 SMBus Transactions
The device supports WRITE and READ transactions. See Table 10 for register address, type (Read/Write, Read
Only), default value and function information.
8.5.5 Writing a Register
To write a register, the following protocol is used (see SMBus 2.0 specification).
1. The Host drives a START condition, the 7-bit SMBus address, and a "0" indicating a WRITE.
2. The Device (Slave) drives the ACK bit ("0").
3. The Host drives the 8-bit Register Address.
4. The Device drives an ACK bit ("0").
5. The Host drive the 8-bit data byte.
6. The Device drives an ACK bit ("0").
7. The Host drives a STOP condition.
The WRITE transaction is completed, the bus goes IDLE and communication with other SMBus devices may
now occur.
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