Texas Instruments MSP430x1xx - Manual (Page 30)

Peripherals
2-4
2.6 Peripherals
Peripheral modules are connected to the CPU through the MAB, MDB, and
interrupt service and request lines. The MAB is usually a 5-bit bus for most of
the peripherals. The MDB is an 8-bit or 16-bit bus. Most of the peripherals
operate in byte format. Modules with an 8-bit data bus are connected by
bus-conversion circuitry to the 16-bit CPU. The data exchange with these
modules must be handled with byte instructions. The SFRs are also handled
with byte instructions. The operation for 8-bit peripherals follows the order
described in Figure 2–2.
Figure 2–2. Bus Connection of Modules/Peripherals
Module/Peripheral
MAB
MDB
Interrupt Request
Interrupt Bus Grant
Interrupt Request
Interrupt Bus Grant
PUC
2.7 Oscillator and Clock Generator
The LFXT1 oscillator is designed for the commonly used 32,768 Hz,
low-current- consumption clock crystal or to be used with a high-speed crystal.
All analog components for the 32,768 Hz oscillator are integrated into the
MSP430; only the crystal needs to be connected with no other external
components required. When using the LFXT1 oscillator with a high-speed
crystal, additional load capacitors are required. Some MSP430 devices have
an additional high-speed crystal oscillator (LFXT2). Refer to the clock chapter
and the specific device data sheets for details.
In addition to the crystal oscillator(s), all MSP430 devices contain a digitally-
controlled RC oscillator (DCO). The DCO is different from RC oscillators found
on other microcontrollers because it is digitally controllable and tuneable.
Clock source selection for peripherals and CPU is very flexible. Most
peripherals are capable of using the 32768-Hz crystal oscillator clock, the
high-speed crystal oscillator clock (where applicable), or the DCO clock. The
CPU is capable of executing from the DCO clock or from either of the two
crystal oscillator clocks. See Chapter 7 for details on the clock system.