Cypress PSoC CY8C23533, Technical Reference Manual

Page: 53 / 410

Document # 001-20559 Rev. *D 53
Supervisory ROM (SROM)
3.3 Clocking
Successful programming and erase operations, on the
Flash, require that the CLOCK and DELAY parameters be
set correctly. To determine the proper value for the DELAY
parameter only, the CPU speed must be considered. How-
ever, three factors should be used to determine the proper
value for CLOCK: operating temperature, CPU speed, and
characteristics of the individual device. Equations and addi-
tional information on calculating the DELAY and CLOCK val-
ues follow.
3.3.1 DELAY Parameter
To determine the proper value for the DELAY parameter, the
CPU speed during the Flash operation must be considered.
Equation 1 displays the equation for calculating DELAY
based on a CPU speed value. In this equation the units for
CPU are hertz (Hz).
Equation 1
Equation 2 shows the calculation of the DELAY value for a
CPU speed of 12 MHz. The numerical result of this calcula-
tion should be rounded to the nearest whole number. In the
case of a 12 MHz CPU speed, the correct value for DELAY
is 86 (0x56).
Equation 2
3.3.2 CLOCK Parameter
The CLOCK parameter must be calculated using different
equations for erase and write operations. The erase value
for CLOCK must be calculated first. In Equation 3, the erase
CLOCK value is indicated by a subscript E after the word
CLOCK and the write CLOCK value is indicated by a sub-
script W after the word CLOCK.
Before either CLOCK value can be calculated, the values for
M, B, and Mult must be determined. These are device spe-
cific values that are stored in the Flash table 3 and are
accessed by way of the TableRead SROM function (see the
“TableRead Function” on page 49 ). If the operating tempera-
ture is at or below 0°C, the cold values should be used. For
operating temperatures at or above 0°C, the hot values
should be used. See
Table 3-11 for more information.
Equations for calculating the correct value of CLOCK for
write operations are first introduced with the assumption that
the CPU speed is 12 MHz.
The equation for calculating the CLOCK value for an erase
Flash operation is shown in Equation 3. In this equation the
T has units of °C.
Equation 3
Using the correct values for B, M, and T, in the equation
above, is required to achieve the endurance specifications
of the Flash. However, for device programmers, where this
calculation may be difficult to perform, the equation can be
simplified by setting T to 0°C and using the hot value for B
and M. This simplification is acceptable only if the total num-
ber of erase write cycles are kept to less than 10 and the
operation is performed near room temperature. When T is
set to 0, Equation 3 simplifies to the following.
Equation 4
Once a value for the erase CLOCK value has been deter-
mined, the write CLOCK value can be calculated. The equa-
tion to calculate the CLOCK value for a write is as follows.
Equation 5
In the equation above, the correct value for Mult must be
determined, based on temperature, in the same way that the
B and M values were determined for Equation 3.
DELAY
100 10
6 –

CPU 80 –

13
----------------------------------------------------------
3 MHz CPU 12 MHz
 

=
DELAY
100 10
6 –

12 10
6

80 –

13
---------------------------------------------------------------
=
CLOCK
E
B
2 M T

256
----------------
– =
CLOCK
E
B =
CLOCK
W
CLOCK
E
Mult

64
----------------------------------------
=