MC9S08GB60A Datasheet, PDF (58/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 4 Memory
R
W
Reset
7
DIVLD
0
6
PRDIV8
5
DIV5
4
DIV4
3
DIV3
2
DIV2
0
0
0
0
0
= Unimplemented or Reserved
Figure 4-4. Flash Clock Divider Register (FCDIV)
1
DIV1
0
0
DIV0
0
Table 4-6. FCDIV Field Descriptions
Field
7
DIVLD
6
PRDIV8
5
DIV[5:0]
Description
Divisor Loaded Status Flag — When set, this read-only status flag indicates that the FCDIV register has been
written since reset. Reset clears this bit and the first write to this register causes this bit to become set regardless
of the data written.
0 FCDIV has not been written since reset; erase and program operations disabled for flash.
1 FCDIV has been written since reset; erase and program operations enabled for flash.
Prescale (Divide) Flash Clock by 8
0 Clock input to the flash clock divider is the bus rate clock.
1 Clock input to the flash clock divider is the bus rate clock divided by 8.
Divisor for Flash Clock Divider — The flash clock divider divides the bus rate clock (or the bus rate clock
divided by 8 if PRDIV8 = 1) by the value in the 6-bit DIV5:DIV0 field plus one. The resulting frequency of the
internal flash clock must fall within the range of 200 kHz to 150 kHz for proper flash operations. Program/erase
timing pulses are one cycle of this internal flash clock, which corresponds to a range of 5 μs to 6.7 μs. The
automated programming logic uses an integer number of these pulses to complete an erase or program
operation. See Equation 4-1 and Equation 4-2. Table 4-7 shows the appropriate values for PRDIV8 and
DIV5:DIV0 for selected bus frequencies.
if PRDIV8 = 0 — f_FCLK = f_Bus ÷ ([DIV5:DIV0] + 1)
if PRDIV8 = 1 — f_FCLK = f_Bus ÷ (8 × ([DIV5:DIV0] + 1))
Eqn. 4-1
Eqn. 4-2
Table 4-7. Flash Clock Divider Settings
f_Bus
20 MHz
10 MHz
8 MHz
4 MHz
2 MHz
1 MHz
200 kHz
150 kHz
PRDIV8
(Binary)
1
0
0
0
0
0
0
0
DIV5:DIV0
(Decimal)
12
49
39
19
9
4
0
0
f_FCLK
192.3 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
150 kHz
Program/Erase Timing Pulse
(5 μs Min, 6.7 μs Max)
5.2 μs
5 μs
5 μs
5 μs
5 μs
5 μs
5 μs
6.7 μs
MC9S08GB60A Data Sheet, Rev. 2
58
Freescale Semiconductor