DOC E10523 Rev.D
Interactive Circuits And Systems Ltd. 2000
43
6.2 Programming the Internal Clock Generator and FPDP Clock
6.2.1 Introduction
The frequency of the ICS-130 internal sampling clock is controlled by programming the
programmable oscillator through the Clock Frequency register of the VMEbus memory
map (see Fig. 4 above). The device is programmed not in engineering units, but by
means of a complex programming word whose construction is described below; a
series of control words must also be written to the device. Data is transferred to the
device serially; it is necessary to write the data to the ICS-130 ADC Clock register one
bit at a time; bit 0 of the register is the relevant bit. Thus the programming sequence
should normally be done by repeatedly writing each control or programming word to the
ADC Clock register, shifting the data right by one bit after each write, until all bits of the
word has been written. An identical operation is used with the FPDP Clock register to
program the FPDP data rate.
Automatic calculation of the oscillator programming word is provided by the
ics130calcFoxWord() function and other functions in the 'C' language function library
supplied with the optional ICS-130 software drivers, available for Solaris 2 and
VxWorks environments. These routines generate a 22-bit formatted programming word
for the oscillator equivalent to the nearest possible frequency to that supplied as input
by the user (in MHz), and also supply the actual frequency represented by the
programming word, as an output.
6.2.2 Programming Summary
The oscillator device contains two registers, the Control Register and the Programming
Word Register. The programming sequence is as follows:
1. Write to Control Register to configure device and prepare the device to receive the
Programming Word.
2. Write Programming Word.
3. Write to Control Register to load Programming Word data into device.
4. Wait at least 10ms for device Voltage Controlled Oscillator (VCO) frequency to
stabilize.
5. Write to Control Register to enable device output of new frequency.
