ICS2595

3

Digital Inputs

The FS0-FS3 pins and the STROBE pin are used to select

the desired operating frequency of the VCLK output from

the 16 pre-programmed/user-programmed selections in

the ICS2595. These pins are also used to load new frequency

data into the registers.

The standard interface for the ICS2595 matches the interface

of the industry standard ICS2494. That is, the FS0-FS3

inputs access the device internals transparently when the

STROBE pin is high.

The digital interface for the ICS2595 (i.e. the FS0-FS3

inputs) may be optionally configured for edge-triggered

or level-activated operation of the STROBE pin. Example

timing requirements for each of the four options are

shown in Figure 1.

The programming sequence has been designed in such a

way that STROBE pin need not be used (as in situations

where the device is connected to the frequency select port

of some VGA chips).

VCLK Output Frequency Selection

To change the VCLK output frequency, simply write the

appropriate data to the ICS2595 FS inputs. The synthesizer

will output the new frequency programmed into that location

after a brief delay (see time-out specifications).

Upon device power-up, the selected frequency will be the

frequency pre-programmed into address 0 until a device

write is performed.

MCLK Output Frequency Selection

The MS0-MS1 pins are used to directly select the desired

operating frequency of the MCLK output from the four

pre-programmed/user-programmed

selections

in

the

ICS2595. These inputs are not latched, nor are they involved

with memory programming operations.

Programming Mode Selection

In order to ensure that reliable programming under all

circumstances, we require that two "nibble" writes be

added to the beginning of the programming sequence that

was previously specified. The new sequence is shown in

Table 1. Note that the FS3 data is "0" for these first two

writes.

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1

Table 1: Programming Sequence

Because the same pins are used for both VCLK frequency

selection and re-programming the device frequency table,

a specific procedure must be observed for selection between

these modes. Device programming is accomplished by

executing a "programming sequence". The latched FS2

input functions as a data input, and the latched FS3 input

functions as a data clock when this mode is activated. As

the latched FS3 data transitions from 0 to 1, the latched

FS2 data is shifted into the register. Note that it is the