
Architecture Overview
SC140 DSP Core Reference Manual
2-5
2.1.3 Program Sequencer Unit (PSEQ)
The PSEQ performs instruction fetch, instruction dispatch, hardware loop control, and exception
processing. The PSEQ controls the different processing states of the SC140 core. The PSEQ consists of
three hardware blocks:
Program dispatch unit (PDU)—Responsible for detecting the execution set out of a one or two fetch
set, and dispatching the execution set’s various instructions to their appropriate execution units
where they are decoded.
Program control unit (PCU)—Responsible for controlling the sequence of the program flow.
Program address generator (PAG)—Responsible for generating the program counter (PC) for
instruction fetch operations, including hardware looping.
The PSEQ implements its functions using the following registers:
PC—Program counter register
SR—Status register
SA0-3—Four start address registers (SA0–SA3)
LC0-3—Four loop counter registers (LC0–LC3)
EMR—Exception and mode register
VBA—Interrupt vector base address register
2.1.4 Enhanced On-Chip Emulator (EOnCE)
The EOnCE module provides a non-intrusive means of interacting with the SC140 core and its peripherals
so that a user can examine registers, memory, or on-chip peripherals as well as define various breakpoints
and read the trace-FIFO. The EOnCE module greatly aids the development of hardware and software on
the SC140 core processor, EOnCE interfacing with the debugging system through on-chip JTAG TAP
controller pins. Refer to Chapter 4, “Emulation and Debug (EOnCE)” for details.
2.1.5 Instruction Set Accelerator Interface
A user-defined instruction set accelerator module provides a means of enhancing the SC140 basic
instruction set with additional instructions. These additional instructions are executed in an external
module connected to the core. The new instructions are added to the SC140 Assembler and Compiler via
intrinsic libraries making application-specific or general-purpose functions available to the user.
A 25-bit instruction bus from the SC140 core to the instruction set accelerator enables the definition and
support of a very rich instruction set. The instruction set accelerator is also connected to the 128-bit
program data bus, providing a large data bandwidth to the main memory system.
2.1.6 Memory Interface
The SC140 core uses a unified memory space. Each address can contain either program information or
data. The exact memory configuration is customizable for each chip containing an SC140 core. Memory
space typically consists of on-chip RAM and ROM that can be expanded off-chip. The memory system
must support two parallel data accesses. However, it may issue stalls due to its specific implementation.
Refer to
Section 2.4, “Memory Interface,”
for further details.
Both internal and external memory configurations are specific to each member of the SC140 family.