ADLINK aTCA-N700 - Manual (Page 48)

aTCA-RN710 User's Guide
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9 I2C
The Zone 3 connector offers two I2C buses. I2C #1 (Conn P1_E2/F2: RTM_SCL/RTM_SDA) is from
the front blade IPMC for IPMB-L connection and I2C #2 (Conn P2_G6/H6: LMP_SCL/LMP_SDA) is
from the front blade switch for the SFP+ port link control.
• I2C #1 is connected only to the MMC on the RTM.
• I2C #2 is connected to the I2C switch for the front blade switch to control SFP related
information (configuration and status gathering) directly or through the I2C IO Buffer.
I2C #2 from the front blade switch is connected to the four I2C HUBs as shown in Figure 9-3 (a). The
I2C HUB on the board is PCA9546A from Phillips. PCA9546A is a 5-channel I2C Hub which enables
extension of an I2C bus by buffering both the data (SDA) and the clock (SCL) lines, for the five buses
of 400pF. The I2C bus capacitance limit of 400pF restricts the number of devices and bus length.
Four I2C buses from each PCA9546A connect to the four SFP+ ports.
The features of the PCA9546A are:
• 1-of-4 bidirectional translating switches
• Supports hot insertion
• 0 Hz to 400 kHz clock frequency
Figure 9-1 PCA9546A Block Diagram
One PCA9547 is used for the retimer configuration, where six I2C buses from the device connect to
the six retimers each.
To collect the status signals such as TXFAULT, INSERT, and RXLOS for the SFP+ ports, three
PCA8575 devices (I2C to I/O) are used on board as shown in Figure 9-3 (b).