GraphiteVPX/GbE 16+4-Port - Managed Carrier Ethernet Switch
Users Guide
Document: CTIM-00461
Revision: 0.02
Page 19 of 26
Connect Tech Inc. 800-426-8979 | 519-836-1291
Date: 2016/10/27
Writing to the I2C Slave Interface
Refer to the NXP PCA9544 datasheet for access details.
The I2C multiplexor is like a ‘gate’ to open an on board I2C bus to access one of three card side busses:
1)
Bus 0 – is a link to one TMP422 (sensor #5) remote temperature sensor (local temp and remote
temperatures of VSC7429 and VSC8512).
2)
Bus 1 – is a direct link with XMC sites I2C system interface
3)
Bus 2 – is a link to 2 TMP101 temperature sensors on the top edge (Sensor 1 and 2)
4)
Bus 3 – is a link to 2 TMP101 temperature sensors on the bottom edge (Sensor 3 and 4)
*Refer to the TI TMP101 datasheet for access and setup of ALERT pin interrupt to the PCA9544. A Thermal
Alert LED is accessible on the solder side of the card if a visual indicator is required.
Reading from the I2C devices
When reading from the I2C slave interface, the last value stored in the command register by a write operation
is used to determine which command to respond to. To change the command for a read operation, a new
command must be written to the command register. This is accomplished by issuing an I2C slave address byte
with the R/W# bit LOW, followed by the command byte. The master can then generate a START condition
and send the I2C slave address byte with the R/W# bit HIGH to initiate a read command. If repeated reads
from the same register are required it is not necessary to continually send the command byte. The slave I2C
interface will remember the original command value until it is changed by the next write operation.
Example XML code to open the I2C mux and access the temperature sensors using the Totalphase Aardvark™
USB to I2C controller can be provided by request.