ICS2694

Integrated Circuit Systems, Inc. ICS2694 Motherboard Clock Generator Description The ICS2694 Motherboard Clock Generator is an integrated circuit using PLL and VCO technology to generate virtually all the clock signals required in a PC. The use of the device can be generalized to satisfy the timing needs of most digital systems by reprogramming the VCO or reconfiguring the counter stages which derive the output frequencies from the VCO’s. The primary VCO is customarily used to generate the CPU clock and is so labeled on the ICS2694. Pre-programmed frequency sets are listed on page 6. These choices were made to match the major microprocessor families. CPUSEL (0-3) allow the user to select the appropriate frequency for the application. Due to the filter in the phase-locked loop, the CPUCLK will move in a linear fashion from one frequency to a newlyselected frequency without glitches. If a fixed CPUCLK value is desired, CPUSEL (0-3) may be hard wired to the desired address with STROBE tied high. (It has a pull-up.) For board test and debug, pulling OUTPUTE to Ground will tristate all the outputs. Features Low cost - eliminates multiple oscillators and Count Down Logic Primary VCO has 16 Mask Programmable frequencies (normally CPU clock) Secondary VCO has 1 Mask Programmable frequency (usually 96 MHz) Pre-programmed versions for typical PC applications 10 Outputs in addition to the primary CPU clock Capability to reconfigure counter stages to change the frequ...