SMJ320F240 Datasheet, PDF (31/99 Pages) Texas Instruments – DSP CONTROLLER

SMJ320F240
DSP CONTROLLER
SGUS029 – APRIL 1999
’F240 DSP core CPU
The SMJ320F240 devices use an advanced Harvard-type architecture that maximizes processing power by
maintaining two separate memory bus structures — program and data — for full-speed execution. This multiple
bus structure allows data and instructions to be read simultaneously. Instructions support data transfers
between program memory and data memory. This architecture permits coefficients that are stored in program
memory to be read in RAM, thereby eliminating the need for a separate coefficient that are ROM. This, coupled
with a four-deep pipeline, allows the ’F240 devices to execute most instructions in a single cycle.
status and control registers
Two status registers, ST0 and ST1, contain the status of various conditions and modes. These registers can
be stored into data memory and loaded from data memory, thereby allowing the status of the machine to be
saved and restored for subroutines.
The load status register (LST) instruction is used to write to ST0 and ST1. The store status register (SST)
instruction is used to read from ST0 and ST1 — except for the INTM bit, which is not affected by the LST
instruction. The individual bits of these registers can be set or cleared when using the SETC and CLRC
instructions. Figure 10 shows the organization of status registers ST0 and ST1, indicating all status bits
contained in each. Several bits in the status registers are reserved and are read as logic 1s. Table 11 lists status
register field definitions.
15
13 12 11 10
9
8
7
6
5
4
3
2
1
0
ST0
ARP
OV OVM 1 INTM
DP
15
13 12 11 10
9
8
7
6
5
4
3
21
0
ST1
ARB
CNF TC SXM C
1
1
1
1
XF
1
1
PM
Figure 10. Status and Control Register Organization
FIELD
ARB
ARP
C
CNF
DP
INTM
Table 11. Status Register Field Definitions
FUNCTION
Auxiliary register pointer buffer. When the ARP is loaded into ST0, the old ARP value is copied to the ARB except during an LST
instruction. When the ARB is loaded by way of an LST #1 instruction, the same value is also copied to the ARP.
Auxiliary register (AR) pointer. ARP selects the AR to be used in indirect addressing. When the ARP is loaded, the old ARP value
is copied to the ARB register. ARP can be modified by memory-reference instructions when using indirect addressing, and by the
LARP, MAR, and LST instructions. The ARP is also loaded with the same value as ARB when an LST #1 instruction is executed.
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.0
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.
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 and IACK also set 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.
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