8.5.2 Writing to and Reading from the Global/Shared/Channel Registers

The DS250DF810 has 3 types of registers:

1) Global Registers – These registers can be accessed at any time and are used to select individual channel registers, the shared registers or to read back the TI ID and version information.

2) Shared Registers – These registers are used for device-level configuration, status read back or control.

3) Channel Registers – These registers are used to control and configure specific features for each individual channel. All channels have the same channel register set and can be configured independent of each other.

The global registers can be accessed at any time, regardless of whether the shared or channel register set is selected. The DS250DF1810 global registers are located on addresses 0xEF-0xFF. The function of the global registers falls into the following categories:

• Channel selection and share enabling – Registers 0xFC and 0xFF
• Device and version information – Registers 0xEF-0xF3
• Reserved/unused registers – all other addresses

Register 0xFF[5:4] is used to select the share registers of either Quad 0 (channels 0-3) or Quad 1 (channels 4-7).

Register 0xFC is used to select the channel registers to be written to. To select a channel, write a 1 to its corresponding bit in register 0xFC. Note that more than one channel may be written to by setting multiple bits in register 0xFC. However, when performing an SMBus read transaction only one channel can be selected at a time. If multiple channels are selected when attempting to perform an SMBus read, the device will return 0x00.

Register 0xFF bit 1 can be used to perform broadcast register writes to all channels. A single channel read-modify broadcast write type commands can be accomplished by setting register 0xFF to 0x03 and selecting a single channel in register 0xFC. This type of configuration allows for the reading of a single channel's register information and then writing to all channels with the modified value. Register 0xFF bit 0 is used to select the shared register page or the channel register page for the channels selected in register 0xFC.

TI repeaters/retimers have a vendor ID register (0xFE) which will always read back 0x03. In addition, there are three device ID registers (0xF0, 0xF1, and 0xF3). These are useful to verify that there is a good SMBus connection between the SMBus master and the DS250DF810.