Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller TSSOP 28 16-Bit 16 MHz I/O number 24

CPU Registers

www.ti.com

Figure 3-6. Status Register Bits

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

OSC CPU

Reserved V SCG1 SCG0 GIE N Z C

OFF OFF

rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0 rw-0

Table 3-1 describes the status register bits.

Table 3-1. Description of Status Register Bits

Bit Description

V Overflow bit. This bit is set when the result of an arithmetic operation overflows the signed-variable range.

Set when:

ADD(.B),ADDC(.B)

Positive + Positive = Negative

Negative + Negative = Positive

Otherwise reset

Set when:

SUB(.B),SUBC(.B),CMP(.B)

Positive – Negative = Negative

Negative – Positive = Positive

Otherwise reset

SCG1 System clock generator 1. When set, turns off the SMCLK.

SCG0 System clock generator 0. When set, turns off the DCO dc generator, if DCOCLK is not used for MCLK or SMCLK.

OSCOFF Oscillator Off. When set, turns off the LFXT1 crystal oscillator, when LFXT1CLK is not use for MCLK or SMCLK.

CPUOFF CPU off. When set, turns off the CPU.

GIE General interrupt enable. When set, enables maskable interrupts. When reset, all maskable interrupts are disabled.

N Negative bit. Set when the result of a byte or word operation is negative and cleared when the result is not negative.

Word operation: N is set to the value of bit 15 of the result.

Byte operation: N is set to the value of bit 7 of the result.

Z Zero bit. Set when the result of a byte or word operation is 0 and cleared when the result is not 0.

C Carry bit. Set when the result of a byte or word operation produced a carry and cleared when no carry occurred.

3.2.4 Constant Generator Registers CG1 and CG2

Six commonly-used constants are generated with the constant generator registers R2 and R3, without

requiring an additional 16-bit word of program code. The constants are selected with the source-register

addressing modes (As), as described in Table 3-2.

Table 3-2. Values of Constant Generators CG1, CG2

R2 00 – – – – – Register mode

R2 01 (0) Absolute address mode

R2 10 00004h +4, bit processing

R2 11 00008h +8, bit processing

R3 00 00000h 0, word processing

R3 01 00001h +1

R3 10 00002h +2, bit processing

R3 11 0FFFFh -1, word processing

The constant generator advantages are:

• No special instructions required

• No additional code word for the six constants

• No code memory access required to retrieve the constant

CPU SLAU144J–December 2004–Revised July 2013

Submit Documentation Feedback