AX88780_07 Datasheet, PDF (52/55 Pages) ASIX Electronics Corporation – High-Performance Non-PCI Single-Chip 32-bit 10/100M Fast Ethernet Controller

Appendix A3. Synchronous and asynchronous timing selection
AX88780
AX88780 can support synchronous or asynchronous access from host MCU. Below information provides some
references to select clock frequency of host MCU and AX88780.
A3-1. AX88780 is synchronous with host MCU.
The timing selection is suitable for both 32-bit and 16-bit mode.
Frequency
Max 100MHz
Access type
Single or Burst
Valid access timing (OEN/WEN active timing)
Min 5 clocks
A3-2. AX88780 is asynchronous to host MCU.
The timing selection is suitable for both 32-bit and 16-bit mode.
Frequency
Max 100MHz
Access type
Single or Burst
Valid access timing (OEN/WEN active timing)
Min 6 reference clocks (Note)
Note: The reference clock is from OSC, and it’s not the output of host MCU. For instance, if AX88780 runs in
asynchronous mode and refers a 100MHz clock from OSC, whereas MCU runs in 125Mhz environment. In
such condition, MCU must at least offer 60ns (min 6 reference clock of 100Mhz) access timing to AX88780.
The 60ns for MCU is almost reached to 8 clocks (125MHz). We recommend that it is needed to extend the
access timing of MCU to AX88780.
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ASIX ELECTRONICS CORPORATION