ICD2051 Cypress Semiconductor Corp., ICD2051 Datasheet - Page 3

• Manufacturer Part Number: ICD2051
• Description: Dual Programmable Clock Generator
• Manufacturer: Cypress Semiconductor Corp.

ICD2051:1/95
Revision: April 11, 1995
General Considerations
Programming the ICD2051
The desired output frequency is defined via a serial interface,
with a 22-bin number shifted in. The ICD2051 has two pro-
grammable PLLs (CLKA and CLKB), requiring a 22-bit pro-
gramming word (W) to be loaded into each channel indepen-
dently. This word contains 5 fields:
Table 1. Programming Word Bit Fields
The frequency of the programmable oscillator f
mined by these fields as follows:
where f
The value of f
Therefore, for output frequencies below 40 MHz, f
multiplied up into the required range. To accomplish this, a
post-VCO Divisor is selected by setting the values of the Mux field
(M) as follows:
Table 2. Mux Field (M)
The Index field (I) is used to preset the VCO to an appropriate
range. The value for this field should be should be chosen from
Table 3 . (Note that this table is referenced to the VCO frequency
f
(VCO)
Index (I)
P Counter value (P’)
Reserved (R)
Mux (M)
Q Counter value (Q’)
P’=P 3
Q’=Q 2
f
(VCO)
, rather than to the desired output frequency.)
(REF)
=2 x f
Field
000
001
010
100
101
011
110
111
M
=Reference frequency (between 1 MHz 25 MHz)
(REF)
(VCO)
x P/Q
must remain between 40 MHz and 120 MHz.
# of
bits
4
7
1
3
7
MSB (Most Significant Bits)
normally set to logic 1
LSB (Least Significant Bits)
Divisor
128
16
32
64
1
2
4
8
Notes
(VCO)
(VCO)
must be
is deter-
3
Table 3. Index Field (I)
If the desired VCO frequency lies on a boundary in the table
(if it is exactly the upper limit of one entry and the lower limit of
the next) then either index value may be used (since both limits
are tested), but we recommend using the higher one.
To assist with these calculations, Cypress/IC Designs provides
BitCalc (Part #ICD/BCALC), a Windows™ program which automat-
ically generates the appropriate programming words from the us-
er’s reference input and desired output frequencies. The software
also assembles the program words for control and power-down reg-
isters. Contact your local Cypress representative for more informa-
tion.
Programming Constraints
There are five primary programming constraints the user must
be aware of:
Table 4. Programming Constraints
The constraints have to do with trade-offs between optimum
speed and lowest noise, VCO stability and factors affecting the
loop equation. The factors are listed for completeness sake;
however, by using the BitCalc program all of these constraints
become transparent.
ICD2051 Programming Example
The following is an example of the calculations BitCalc per-
forms:
Parameter
0000
0001
0010
0011
0100
0101
0110
1000
1001
1010
1011
1100
1101
0111
1110
1111
f
(REF)
f
f
I
(VCO)
(REF)
Q
P
/Q
Minimum
200 kHz
40 MHz
1 MHz
3
4
105.0
115.0
115.0
115.0
92.1
f
42.5
40.0
47.5
53.5
58.5
62.5
68.5
69.0
82.0
87.0
92.0
(VCO)
(MHz)
105.0
47l.5
120.0
120.0
120.0
42.5
53.5
58.5
62.5
68.5
69.0
82.0
87.0
92.0
92.1
115.0
Maximum
120 MHz
ICD2051
25 MHz
1 MHz
129
130