MSP430C33x, MSP430P337A
MIXED SIGNAL MICROCONTROLLERS
SLAS227A – OCTOBER 1999 – REVISED JUNE 2000
11
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
oscillator and system clock (continued)
The crystal frequency multiplication is achieved with a frequency locked loop (FLL) technique. The factor N is
set to 31 after a power-up clear condition. The FLL technique, in combination with a digital controlled oscillator
(DCO), provides immediate start-up capability together with long term crystal stability. The frequency variation
of the DCO with the FLL inactive is typically 330 ppm, which means that with a cycle time of 1
s the maximum
possible variation is 0.33 ns. For more precise timing, the FLL can be used, which forces longer cycle times if
the previous cycle time was shorter than the selected one. This switching of cycle times makes it possible to
meet the chosen system frequency over a long period of time.
The start-up operation of the system clock depends on the previous machine state. During a PUC, the DCO
is reset to its lowest possible frequency. The control logic starts operation immediately after recognition of PUC.
multiplication
The multiplication operation is supported by a dedicated peripheral module. The module performs 16x16, 16x8,
8x16, and 8x8 bit operations. The module is capable of supporting signed and unsigned multiplication as well
as signed and unsigned multiply and accumulate operations. The result of an operation can be accessed
immediately after the operands have been loaded into the peripheral registers. No additional clock cycles are
required.
digital I/O
Five eight-bit I/O ports (P0 thru P4) are implemented. Port P0 has six control registers, P1 and P2 have seven
control registers, and P3 and P4 modules have four control registers to give maximum flexibility of digital
input/output to the application:
D Individual I/O bits are independently programmable.
D Any combination of input, output, and interrupt conditions is possible.
D Interrupt processing of external events is fully implemented for all eight bits of the P0, P1, and P2 ports.
D Read/write access is available to all registers by all instructions.
The seven registers are:
D Input register
contains information at the pins
D Output register
contains output information
D Direction register
controls direction
D Interrupt edge select
contains input signal change necessary for interrupt
D Interrupt flags
indicates if interrupt(s) are pending
D Interrupt enable
contains interrupt enable pins
D Function select
determines if pin(s) used by module or port
These registers contain eight bits each with the exception of the interrupt flag register and the interrupt enable
register which are 6 bits each. The two least significant bit (LSBs) of the interrupt flag and enable registers are
located in the special function register (SFR). Five interrupt vectors are implemented, one for Port P0.0, one
for Port P0.1, one commonly used for any interrupt event on Port P0.2 to Port P0.7, one commonly used for any
interrupt event on Port P1.0 to Port P1.7, and one commonly used for any interrupt event on Port P2.0 to Port
P2.7.