MC68HC908LB8_05 Datasheet, PDF (131/234 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Input/Output (I/O) Registers
ECGST — External Clock Status Bit
This read-only bit indicates whether or not an external clock source is engaged to drive the system
clock.
1 = An external clock source engaged
0 = An external clock source disengaged
13.8.2 Oscillator Trim Register (OSCTRIM)
Address: $0038
Bit 7
Read:
TRIM7
Write:
Reset:
1
6
TRIM6
0
5
TRIM5
0
4
TRIM4
0
3
TRIM3
0
2
TRIM2
0
1
TRIM1
0
Figure 13-5. Oscillator Trim Register (OSCTRIM)
Bit 0
TRIM0
0
TRIM7–TRIM0 — Internal Oscillator Trim Factor Bits
These read/write bits change the size of the internal capacitor used by the internal oscillator. By
measuring the period of the internal clock and adjusting this factor accordingly, the frequency of the
internal clock can be fine tuned. Increasing (decreasing) this factor by one increases (decreases) the
period by appoximately 0.2% of the untrimmed period (the period for TRIM = $80). The trimmed
frequency is guaranteed not to vary by more than ±5% over the full specified range of temperature and
voltage. The reset value is $80, which sets the frequency to 16 MHz (4.0 MHz bus speed) ±25%.
MC68HC908LB8 Data Sheet, Rev. 1
Freescale Semiconductor
131