QT2022/32 - Data Sheet: DS3051
18.5.4 Reset Timing Recommendations After Powerup
It is recommended to ensure there are no I2C transactions in progress before applying a reset to the QT2022/32.
The reset can interrupt any ongoing I2C transactions and re-initialize the QT2022/32’s I2C bus controller. However,
it will not reset the peripheral I2C device. If an I2C transaction is interrupted by a reset, the peripheral device will
expect the transaction to continue.
After reset the QT2022/32 will initialize the bus as described on page 89. This will clear all I2C transactions, so all
peripheral devices are ready to accept a new command. However, robust firmware should not rely on this feature
to clear the bus.
I2C activity is reported in the NVR Control/Status Register (1.8000h) and DOM Control/Status Register (1.A100h).
Ensure the Command Status fields of both registers do not report “in progress” (bits 3:2 NOT = ‘10’) before apply-
ing a reset.
Refer to AMCC document GAN2072, “Reset Timing Recommendations” for more details.
18.6 MDIO Bus Implementation
Although the MDIO bus is a relatively low-speed bus the transition times can be very fast, so correct implementa-
tion is important. The MDC signal, originating from the Station Manager (STA) on the host system, may or may not
require a pullup resistor depending on implementation. The MDIO does require a pullup.
In a module application, it is recommended that all pullup resistors be placed on the host card. If the pullup resis-
tors are placed in the module, the pullups will act in parallel in a multi-port line card. The total pullup resistance will
be reduced in accordance with the number of populated modules. Thus the pullup resistance will be unpredictable
and, if it is too low, may exceed the current drive capabilities of the driver.
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