TMS320F241FN datasheet(40/116 Pages) TI

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TMS320F243, TMS320F241

DSP CONTROLLERS

SPRS064B – DECEMBER 1997 – REVISED FEBRUARY 1999

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251–1443

Table 14. Status Register Field Definitions (Continued)

FIELD

FUNCTION

Carry bit. C is set to 1 if the result of an addition generates a carry, or reset to 0 if the result of a subtraction generates a borrow.

Otherwise, C is reset after an addition or set after a subtraction, except if the instruction is ADD or SUB with a 16-bit shift. In these

cases, the ADD can only set and the SUB only reset the carry bit, but cannot affect it otherwise. The single-bit shift and rotate

instructions also affect C, as well as the SETC, CLRC, and LST #1 instructions. Branch instructions have been provided to branch

on the status of C. C is set to 1 on a reset.

CNF

On-chip RAM configuration control bit. If CNF is set to 0, the reconfigurable data dual-access RAM blocks are mapped to data

space; otherwise, they are mapped to program space. The CNF can be modified by the SETC CNF, CLRC CNF, and LST #1

instructions. RS sets the CNF to 0.

Data memory page pointer. The 9-bit DP register is concatenated with the seven LSBs of an instruction word to form a direct

memory address of 16 bits. DP can be modified by the LST and LDP instructions.

INTM

Interrupt mode bit. When INTM is set to 0, all unmasked interrupts are enabled. When set to 1, all maskable interrupts are disabled.

INTM is set and reset by the SETC INTM and CLRC INTM instructions. RS also sets INTM. INTM has no effect on the unmaskable

RS and NMI interrupts. Note that INTM is unaffected by the LST instruction. This bit is set to 1 by reset. It is also set to 1 when

a maskable interrupt trap is taken.

Overflow flag bit. As a latched overflow signal, OV is set to 1 when overflow occurs in the arithmetic logic unit (ALU). Once an

overflow occurs, the OV remains set until a reset, BCND/D on OV/NOV, or LST instructions clear OV.

OVM

Overflow mode bit. When OVM is set to 0, overflowed results overflow normally in the accumulator. When set to 1, the accumulator

is set to either its most positive or negative value upon encountering an overflow. The SETC and CLRC instructions set and reset

this bit, respectively. LST can also be used to modify the OVM.

Product shift mode. If these two bits are 00, the multiplier’s 32-bit product is loaded into the ALU with no shift. If PM = 01, the PREG

output is left-shifted one place and loaded into the ALU, with the LSB zero-filled. If PM = 10, PREG output is left-shifted by four

bits and loaded into the ALU, with the LSBs zero-filled. PM = 11 produces a right shift of six bits, sign-extended. Note that the PREG

contents remain unchanged. The shift takes place when transferring the contents of the PREG to the ALU. PM is loaded by the

SPM and LST #1 instructions. PM is cleared by RS.

SXM

Sign-extension mode bit. SXM = 1 produces sign extension on data as it is passed into the accumulator through the scaling shifter.

SXM = 0 suppresses sign extension. SXM does not affect the definitions of certain instructions; for example, the ADDS instruction

suppresses sign extension regardless of SXM. SXM is set by the SETC SXM and reset by the CLRC SXM instructions, and can

be loaded by the LST #1 instruction. SXM is set to 1 by reset.

Test/control flag bit. TC is affected by the BIT, BITT, CMPR, LST #1, and NORM instructions. TC is set to a 1 if a bit tested by BIT

or BITT is a 1, if a compare condition tested by CMPR exists between AR (ARP) and AR0, if the exclusive-OR function of the two

most significant bits (MSBs) of the accumulator is true when tested by a NORM instruction. The conditional branch, call, and return

instructions can execute based on the condition of TC.

XF pin status bit. XF indicates the state of the XF pin, a general-purpose output pin. XF is set by the SETC XF and reset by the

CLRC XF instructions. XF is set to 1 by reset.

central processing unit

The TMS320x24x central processing unit (CPU) contains a 16-bit scaling shifter, a 16 x 16-bit parallel multiplier,

a 32-bit central arithmetic logic unit (CALU), a 32-bit accumulator, and additional shifters at the outputs of both

the accumulator and the multiplier. This section describes the CPU components and their functions. The

functional block diagram shows the components of the CPU.

input scaling shifter

The TMS320x24x provides a scaling shifter with a 16-bit input connected to the data bus and a 32-bit output

connected to the CALU. This shifter operates as part of the path of data coming from program or data space

to the CALU and requires no cycle overhead. It is used to align the 16-bit data coming from memory to the 32-bit

CALU. This is necessary for scaling arithmetic as well as aligning masks for logical operations.

The scaling shifter produces a left shift of 0 to 16 on the input data. The LSBs of the output are filled with zeros;

the MSBs can either be filled with zeros or sign-extended, depending upon the value of the SXM bit

(sign-extension mode) of status register ST1. The shift count is specified by a constant embedded in the

status and control registers (continued)

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