ARM ARM DUI 0224I

Programmer’s Reference

4.3.4 Oscillator registers, SYS_OSCx

The oscillator registers, SYS_OSC0 to SYS_OSC4, at

0x1000000C

–

0x1000001C

are

read/write registers that control the frequency of the clocks generated by the ICS307

programmable oscillators. A serial interface transfers the values in the registers to the

programmable oscillators when a reset occurs.

Note

If the DEV CHIP RECONFIG pushbutton is pressed, the contents of the

SYS_OSCRESETx registers are copied into the SYS_OSCx registers before the

contents are transmitted to the programmable oscillators. This allows the clock

frequencies and the clock divider ratios to be changed at the same time.

Figure 4-8 shows the bit assignment of the registers.

Figure 4-8 Oscillator Register, SYS_OSCx

Table4-6 lists the details o f the SYS_OSCx registers. For more detail on bit values, see

ICS307 programmable clock generators on page3-48 and Clock rate restrictions on

page B-5.

Note

Before writing to a SYS_OSC register, unlock it by writing the value

0x0000A05F

to the

SYS_LOCK register. After writing the SYS_OSC register, relock it by writing any

value other than

0x0000A05F

to the SYS_LOCK register.

Table4-6 Oscillator Register, SYS_OSCx bit assignment

Bits Access Description

[31:19] Reserved, Use read-modify-write to preserve value.

[18:16] Read/write DIVIDE[2:0], output divider select

[15:9] Read/write RDW[6:0], reference divider word

[8:0] Read/write VDW[8:0], VCO divider word