
MPC9229
386
FREESCALE SEMICONDUCTOR ADVANCED CLOCK DRIVERS DEVICE DATA
Substituting N for the four available values for N (1, 2, 4, 8)
yields:
Example Frequency Calculation for an 16 MHz Input
Frequency
If an output frequency of 131 MHz was desired the following
steps would be taken to identify the appropriate M and N values.
According to Table 8, 131 MHz falls in the frequency set by an
value of 2 so N[1:0] = 01. For N = 2 the output frequency is
fOUT = M ÷ 2 and M = fOUT x 2. Therefore M = 2 x 131 = 262, so
M[8:0] = 100000110. Following this procedure a user can
generate any whole frequency between 25 MHz and 400 MHz.
Note than for N > 2 fractional values of can be realized. The size
of the programmable frequency steps (and thus the indicator of
the fractional output frequencies achievable) will be equal to:
fSTEP = fXTAL ÷ 16 ÷ N
APPLICATIONS INFORMATION
Using the Parallel and Serial Interface
The M and N counters can be loaded either through a parallel
or serial interface. The parallel interface is controlled via the
P_LOAD signal such that a LOW-to-HIGH transition will latch
the information present on the M[8:0] and N[1:0] inputs into the
M and N counters. When the P_LOAD signal is LOW, the input
latches will be transparent and any changes on the M[8:0] and
N[1:0] inputs will affect the fOUT output pair. To use the serial
port, the S_CLOCK signal samples the information on the
S_DATA line and loads it into a 14-bit shift register. Note that the
P_LOAD signal must be HIGH for the serial load operation to
function. The Test register is loaded with the first three bits, the
N register with the next two and the M register with the final
eight bits of the data stream on the S_DATA input. For each
register the most significant bit is loaded first (T2, N1, and M8).
A pulse on the S_LOAD pin after the shift register is fully loaded
will transfer the divide values into the counters. The
HIGH-to-LOW transition on the S_LOAD input will latch the new
divide values into the counters. Figure 4 illustrates the timing
diagram for both a parallel and a serial load of the MPC9229
synthesizer. M[8:0] and N[1:0] are normally specified once at
power-up through the parallel interface, and then possibly again
through the serial interface. This approach allows the
application to come up at one frequency and then change or
fine-tune the clock as the ability to control the serial interface
becomes available.
Using the Test and Diagnosis Output TEST
The TEST output provides visibility for one of the several
internal nodes as determined by the T[2:0] bits in the serial
configuration stream. It is not configurable through the parallel
interface. Although it is possible to select the node that
represents fOUT, the CMOS output is not able to toggle fast
enough for higher output frequencies and should only be used
for test and diagnosis. The T2, T1, and T0 control bits are preset
to ‘000' when P_LOAD is LOW so that the PECL fOUT outputs
are as jitter-free as possible. Any active signal on the TEST
output pin will have detrimental affects on the jitter of the PECL
output pair. In normal operations, jitter specifications are only
guaranteed if the TEST output is static. The serial configuration
port can be used to select one of the alternate functions for this
pin. Most of the signals available on the TEST output pin are
useful only for performance verification of the MPC9229 itself.
However the PLL bypass mode may be of interest at the board
level for functional debug. When T[2:0] is set to 110, the
MPC9229 is placed in PLL bypass mode. In this mode the
S_CLOCK input is fed directly into the M and N dividers. The N
divider drives the fOUT differential pair and the M counter drives
the TEST output pin. In this mode the S_CLOCK input could be
used for low speed board level functional test or debug.
Bypassing the PLL and driving fOUT directly gives the user more
control on the test clocks sent through the clock tree. Figure 6
shows the functional setup of the PLL bypass mode. Because
the S_CLOCK is a CMOS level, the input frequency is limited to
200 MHz. This means the fastest the fOUT pin can be toggled
via the S_CLOCK is 100 MHz as the divide ratio of the Post-PLL
divider is 2 (if N = 1). Note that the M counter output on the
TEST output will not be a 50% duty cycle.
Table 8. Output Frequency Range for fXTAL = 16 MHz
N
fOUT
fOUT Range
fOUT Step
1
0
Value
0
1
M
200 – 400 MHz
1 MHz
0
1
2
M
÷ 2
100 – 200 MHz
500 kHz
1
0
4
M
÷ 4
50 – 100 MHz
250 kHz
1
8
M
÷ 8
25 – 50 MHz
125 kHz
Table 9. Test and Debug Configuration for TEST
T[2:0]
TEST Output
T2
T1
T0
0
14-bit shift register out1
1. Clocked out at the rate of S_CLOCK
0
1
Logic 1
0
1
0
fXTAL ÷ 16
0
1
M-Counter out
1
0
fOUT
1
0
1
Logic 0
1
0
M-Counter out in PLL-bypass mode
1
fOUT ÷ 4
Table 10. Debug Configuration for PLL Bypass1
1. T[2:0] = 110. AC specifications do not apply in PLL bypass mode
Output
Configuration
fOUT
S_CLOCK
÷ N
TEST
M-Counter out2
2. Clocked out at the rate of S_CLOCK
÷ (4 N)
MPC9229
400 MHz Low Voltage PECL Clock Synthesizer
NETCOM
IDT 400 MHz Low Voltage PECL Clock Synthesizer
Freescale Timing Solutions Organization has been acquired by Integrated Device Technology, Inc
MPC9229
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