Texas Instruments MSP430x11x1 oscillator and system clock continued, Clock Signals, digital I/O

MSP430x11x1

MIXED SIGNAL MICROCONTROLLER

SLAS241C ± SEPTEMBER 1999 ± REVISED JUNE 2000

oscillator and system clock (continued)

	DIVA
	2
LFXT1CLK		ACLK
	/1, /2, /4, /8
OSCOff XTS		Auxiliary Clock
XIN	ACLKGEN
SELM	DIVM CPUOff
LFXT1 OSCILLATOR
2	2

3
0,1	/1, /2, /4, /8, Off	MCLK
XOUT
2		Main System Clock
DCOCLK	MCLKGEN

VCCVCC

Rsel SCG0	DCO	MOD
	3	5	SELS	DIVS	SCG1
				2

	0	Digital Controlled Oscillator (DCO)	0
	DC
		+	/1, /2, /4, /8, Off	SMCLK
	Generator
		Modulator (MOD)		Subsystem Clock
	1		1
P2.5/Rosc
	DCGEN	DCOMOD	SMCLKGEN
	DCOR
		The DCO-Generator is connected to pin P2.5/Rosc if DCOR control bit is set.
		The port pin P2.5/Rosc is selected if DCOR control bit is reset (initial state).

P2.5

Figure 3. Clock Signals

Two clock sources, LFXT1CLK and DCOCLK, can be used to drive the MSP430 system. The LFXT1CLK is generated from the LFXT1 crystal oscillator. The LFXT1 crystal oscillator can operate in three modesÐlow frequency (LF), moderate frequency (XT1), and external input mode. The LFXT1 crystal oscillator may be switched off when it is not in use.

DCOCLK is generated from the DCO. The nominal DCO frequency is defined by the dc generator and can be set by one external resistor, or can be set to one of eight values with integrated resistors. Additional adjustments and modulations of DCOCLK are possible by software manipulation of registers in the DCO module. DCOCLK is stopped automatically when it is not used by the CPU or peripheral modules. The dc generator can be shut down with the SCG0 bit to realize additional power savings when DCOCLK is not in use.

NOTE:

The system clock generator always starts with the DCOCLK selected for MCLK (CPU clock) to ensure proper start of program execution. The software defines the final system clock generation through control bit manipulation.

digital I/O

There are two eight-bit I/O ports, port P1 and port P2 ± implemented (11x1 parts only have six port P2 I/O signals available on external pins). Both ports, P1 and P2, have seven control registers to give maximum flexibility of digital input/output to the application:

•All individual I/O bits are programmable independently.

•Any combination of input, output, and interrupt conditions is possible.

•Interrupt processing of external events is fully implemented for all eight bits of port P1 and for six bits of port P2.

•Read/write access to all registers with all instructions

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