ICS9161A Datasheet, PDF (6/15 Pages) Integrated Circuit Systems – Dual Programmable Graphics Frequency Generator

ICS9161A
The serial data register is exactly 24 bits long, enough to
accept the data being sent. The stop bit acts as a load command
that passes the contents of the Serial Data Register into the
register indicated by the three address bits. If a stop bit is not
received after the serial register is full, and more data is sent,
all data in the register is ignored and an error issued. If correct
data is received, then the unlocking mechanism re-arms, all
data in the serial data register is ignored, and an error is
issued.
ERROUT# Operation
Any error in programming the ICS9161A is signaled by
ERROUT#. When the pin goes low, an error has been detected.
It stays low until the next unlock sequence. The signal is
invoked for any of the following errors: incorrect start bit,
incorrect data encoding, incorrect length of data word, and
incorrect stop bit.
Programming the ICS9161A
The ICS9161A has a wide operating range, but it is
recommended that it is operated within the following limits:
3.15V< V_DD <5.25V
V_DD supply voltage
1 MHz <F_REF <60 MHz
200 kHz <F_REF/M <5 MHz
50 MHz < F_VCO <120 MHz
F_CLK ≤ 120 MHz
F_REF=Input Reference
Frequency
M=Reference divide 3
to 129
F_VCO=VCO output
frequency
F_CLK=output frequency
The frequency of the programmable oscillator FVCO is
determined by the following fields:
Field
Index (I)
N counter value (N')
Mux (R)
M counter value (M')
# of Bits
4
7
3
7
Where the least significant bit is the last bit of M and the most
significant bit is the first bit of I.
The equations used to determine the oscillator frequency are:
N=N’ + 3 M=M’ + 2
F_VCO=Prescale • N/M • F_REF
where 3 ≤ M ≤ 129 and 4 ≤ N ≤ 130
and prescale=2 or 4, as set in the control register
(Where N is the VCO divider & M is the reference divider)
The value of F_VCO must remain between 50 MHz and 120 MHz.
As a result, for output frequencies below 50 MHz, F_VCO must
be brought into range. To achieve this, an output divisor is
selected by setting the values of the Mux Field (R) as follows:
Output Divisor
R
Divisor
000
1
001
2
010
4
011
8
100
16
101
32
110
64
111
128
Unlike the ICD2061A, the ICS9161A’s VCO does not
require tuning to place it in certain ranges. The ICS9161A’s
VCO will operate from 50 MHz to 120 MHz without adjusting
the VCO gain. However, to maintain compatibility, the I bits
are programmed as in the ICD2061A.
These bits are dummy bits except for the following two cases:
Index Field (I)
I
1110
1111
VCLK F_VCO
Turn off VCLK
Mux MCLK to VLCK
MCLK F_VCO
50 - 120 MHz
50 - 120 MHz
When the index field is set to 1111, VCLK is turned off and
both channels run from the same MCLK VCO. This is done in
an effort to reduce jitter, which may increase when VCOs run
at 2ⁿ multiples of one another. If the two outputs have to be
multiples of one another, it is best to mux MCLK over to the
output of the VCLK VCO and to power-down the VCLK VCO.
The multiplexed frequency will be divided down by the correct
divisor (M) and output on VCLK.
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