mc9s08ac16 Freescale Semiconductor, Inc, mc9s08ac16 Datasheet - Page 57

• Manufacturer Part Number: mc9s08ac16
• Description: Hcs08 Microcontrollers 8-bit Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

4.6
The FLASH module has nine 8-bit registers in the high-page register space, three locations in the
nonvolatile register space in FLASH memory which are copied into three corresponding high-page control
registers at reset. There is also an 8-byte comparison key in FLASH memory. Refer to
Table 4-4
control bits only by their names. A Freescale-provided equate or header file normally is used to translate
these names into the appropriate absolute addresses.
4.6.1
Bit 7 of this register is a read-only status flag. Bits 6 through 0 may be read at any time but can be written
only one time. Before any erase or programming operations are possible, write to this register to set the
frequency of the clock for the nonvolatile memory system within acceptable limits.
Table 4-7
Freescale Semiconductor
Reset
PRDIV8
DIV[5:0]
DIVLD
Field
5:0
7
6
W
R
FLASH Registers and Control Bits
for the absolute address assignments for all FLASH registers. This section refers to registers and
shows the appropriate values for PRDIV8 and DIV5:DIV0 for selected bus frequencies.
FLASH Clock Divider Register (FCDIV)
DIVLD
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
0
7
= Unimplemented or Reserved
PRDIV8
if PRDIV8 = 1 — f
if PRDIV8 = 0 — f
0
6
Figure 4-5. FLASH Clock Divider Register (FCDIV)
Table 4-6. FCDIV Register Field Descriptions
Equation
MC9S08AC16 Series Data Sheet, Rev. 0
DIV5
0
5
FCLK
4-1,
FCLK
Equation
= f
PRELIMINARY
= f
Bus
DIV4
Bus
0
4
÷ (8 × ([DIV5:DIV0] + 1))
4-2, and
Description
÷ ([DIV5:DIV0] + 1)
Table
DIV3
3
0
4-6.
DIV2
0
2
DIV1
Table 4-3
0
1
Chapter 4 Memory
and
Eqn. 4-1
Eqn. 4-2
DIV0
0
0
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