MC68HC05JJ6 Datasheet, PDF (70/216 Pages) Freescale Semiconductor, Inc – General Release Specification Microcontrollers

Operating Modes
6.3 Oscillator Source
The MCU can be clocked by either an internal low-power oscillator
(LPO) without external components or by an external pin oscillator
(EPO) which uses external components. The enable and selection of the
clock source is determined by the state of the oscillator select bits (OM1
and OM2) in the interrupt status and control register (ISCR) as shown in
Figure 6-1.
$000D
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
0
IRQF
0
0
0
IRQE OM2 OM1
R
IRQR
1
1
0
0
0
0
U
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 6-1. IRQ Status and Control Register (ISCR)
IRQE — External Interrupt Request Enable
This read/write bit enables external interrupts. Refer to Section 4.
Interrupts for more details.
OM1 and OM2 — Oscillator Selects
These bits control the selection and enabling of the oscillator source
for the MCU. One choice is the internal LPO and the other oscillator
is the EPO which is common to most MC68HC05 MCU devices. The
EPO uses external components like filter capacitors and a crystal or
ceramic resonator and consumes more power than the LPO. The
selection and enable conditions for these two oscillators are shown in
Table 6-1. Reset clears OM1 and sets OM2, which selects the LPO
and disables the EPO.
.
Table 6-1. Oscillator Selection
OM2 OM1
0
0
0
1
1
0
1
1
Oscillator
Selected
Internal
External
Internal
Internal
Internal
Low-Power
Oscillator (LPO)
Enabled
Disabled
Enabled
Enabled
External Pin
Oscillator
(EPO)
Power
Consumption
Disabled
Lowest
Enabled
Normal
Disabled
Lowest
Enabled
Normal
General Release Specification
70
Operating Modes
MC68HC05JJ6/MC68HC05JP6 — Rev. 3.2
Freescale Semiconductor