Local bus clock domain (CLKIN) | Cypress Semiconductor
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Local bus clock domain (CLKIN)
- Can the PCI-DP local bus run above 50MHz?
- Does CLKIN have to be free running?
- Can I use two independent clocks for the PCI-DP and the local bus?
The clock for the local bus interface is called CLKIN. The maximum local bus frequency of the PCI-DP is 50MHz. There are no additional mode options to allow this frequency to exceed our specified limit.
CLKIN has to be free running and continous before the PCI-DP is released from reset. If you look on page 7 of the datasheet, you will see that a valid CLKIN signal is required during start-up to properly configure the PCI-DP. This is because the operation registers reside in the local bus clock domain. Customers who gated or turned on the clock after powering up the computer introduced glitches in the CLKIN signal which caused the PC to hang. In addition, CLKIN should sync up to the local processor connected to the PCI-DP. Running two different clock domains to the local processor and the chip can cause problems. The PCI-DP is a synchronous device and depends upon accurate timing synchrnonization with the DSP.