M68HC08 datasheet(90/188 Pages) FREESCALE

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Internal Clock Generator Module (ICG)

Data Sheet

MC68HC908RF2 — Rev. 4.0

Internal Clock Generator Module (ICG)

MOTOROLA

6.7.2 ICG Multiplier Register

N6–N0 — ICG Multiplier Factor Bits

These read/write bits change the multiplier used by the internal

clock generator. The internal clock (ICLK) will be

(307.2 kHz

±25 percent) * N. A value of $00 in this register is interpreted the

same as a value of $01. This register cannot be written when the CMON bit is

set. Reset sets this factor to $15 (decimal 21) for default frequency of 6.45 MHz

±25 percent (1.613 MHz ±25 percent bus).

6.7.3 ICG Trim Register

TRIM7–TRIM0 — ICG Trim Factor Bits

These read/write bits change the size of the internal capacitor used by the

internal clock generator. By testing the frequency of the internal clock and

incrementing or decrementing this factor accordingly, the accuracy of the

internal clock can be improved to

±2 percent. Incrementing this register by 1

decreases the frequency by 0.195 percent of the unadjusted value.

Decrementing this register by one increases the frequency by 0.195 percent.

This register cannot be written when the CMON bit is set. Reset sets these bits

to $80, centering the range of possible adjustment.

NOTE:

It is recommended that the user preserve a copy of the contents of the ICG trim

Address $7FEF is reserved for an optional factory-determined ICG trim value.

Consult with a local Motorola representative for more information and availability of

this option.

Address: $0037

Bit 7

654321

Bit 0

Read:

N6N5

N3N2N1N0

Write:

Reset:

00010101

= Reserved

Figure 6-12. ICG Multiplier Register (ICGMR)

Address: $0038

Bit 7

654321

Bit 0

Read:

TRIM7

TRIM6

TRIM5

TRIM4

TRIM3

TRIM2

TRIM1

TRIM0

Write:

Reset:

10000000

Figure 6-13. ICG Trim Register (ICGTR)

Freescale Semiconductor, Inc.

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