Microgate SyncLink USB - SyncLink USB Frequency Synthesizer

Frequency Synthesizer
The serial controller requires a base clock for the baud rate generator (BRG) to create data clocks. A data
clock may be output on the AUXCLK serial signal or used internally for a synchronous data clock,
asynchronous sampling clock or for DPLL clock recovery.
The SyncLink USB has a fixed frequency crystal that drives the reference clock input of a variable
frequency synthesizer. The default crystal frequency is 14.7456MHz, and on power up the synthesizer
outputs the same frequency on CLK1 (pin 8) which is used as the standard base clock by the serial
controller. Other crystal frequencies are available by special order.
The serial controller GPIO signals program the synthesizer through an SPI interface and selects between
synthesizer outputs. The base clock is common to all ports in the controller.
The synthesizer is made by Integrated Device Technologies (IDT). Refer to the documentation available
from IDT (www.idt.com) for details on programming the synthesizer. An IDT supplied program
(Versaclock 2) generates programming data (132 bit value) for a specific frequency output. Versaclock 3
and later software does not support the ICS307. Contact IDT to get a copy of Versaclock 2. The CLK1 and
CLK3 outputs of the synthesizer are used and CLK2 is unconnected. Sample code for programming the
synthesizer through the GPIO portion of the serial API is available from MicroGate. The maximum
synthesizer frequency supported by the serial controller is 66MHz.
Fixed Frequency Crystal
(Default 14.7456MHz)
Reference Clock
IDT ICS307-3 Frequency
Synthesizer
Data In (DI)
Select (CS)
Clock (CLK)
MicroGate Serial Controller
GPIO[20] Data
GPIO[21] Chip Select
GPIO[22] Clock
Clock Select
0 = standard
1 = synthesizer
GPIO[23] (clock select)
Base Clock Input
CLK1 (Pin 8)
CLK3 (Pin 14)
SPI Interface