MPC555
/
MPC556
CDR MoneT FLASH EEPROM
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
19-28
Pulse
Width = System Clock Period
•
R
•
2
N
•
M
Where:
R = Clock Scaling
N = 5 + CLKPE[0:1] + ((PE | CSC)
•
10)
M = 1 + CLKPM[0:6]
The following subsections explain how the values for R, N, and M are determined.
19.7.3 System Clock Scaling
The first term of the pulse width timing equation is the clock scaling, R. The value of R
is determined by the system clock range (SCLKR) field. SCLKR defines the pulse tim-
er’s base clock using the system clock. Use
the system clock frequency. The system clock period is multiplied by the clock scaling
value to generate a 83.3-ns to 125-ns scaled clock. This scaled clock is used to run
the charge pump submodule and the next functional block of the timing control.
NOTE
The minimum specified system clock frequency for performing pro-
gram and erase operations is 8.0 MHz. The CMF EEPROM does not
have any means to monitor the system clock frequency and will not
prevent program or erase operation at frequencies below 8.0 MHz.
Attempting to program or erase the CMF EEPROM at system clock
frequencies lower than 8.0 MHz will not damage the device if the
maximum pulse times and total times are not exceeded. While some
bits in the CMF EEPROM array may change state if programmed or
erased at system clock frequencies below 8.0 MHz, the full program
or erase transition is not ensured.
WARNING
Never stop the U-bus clock or alter its frequency during a program or
erase operation. Changing the clock frequency during a program or
erase operation results in inaccurate pulse widths and variations in
the charge pump output. This includes loss of system clock/PLL.
Table 19-12 System Clock Range
SCLKR[0:2]
System Clock Frequency (MHz)
Clock Scaling (R)
Minimum
Maximum
000
Not for customer use
.
Program and erase timing control
not specified and pulse is not terminated by the timer con-
trol. Recovery time is specified to be 128 clocks.
1
001
8
12
1
010
12
18
3/2
011
18
24
2
100
24
36
3
101
36
40
4
110 and 111
Reserved by Motorola for future use
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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