Functional Overview
3.2.2 Memory Bus (Harvard Bus Architecture)
As with many DSP type devices, multiple busses are used to move data between the memories and
peripherals and the CPU. The C28x memory bus architecture contains a program read bus, data read bus
and data write bus. The program read bus consists of 22 address lines and 32 data lines. The data read and
write busses consist of 32 address lines and 32 data lines each. The 32-bit-wide data busses enable single
cycle 32-bit operations. The multiple bus architecture, commonly termed “Harvard Bus”, enables the C28x to
fetch an instruction, read a data value and write a data value in a single cycle. All peripherals and memories
attached to the memory bus will prioritize memory accesses. Generally, the priority of Memory Bus accesses
can be summarized as follows:
†
Highest:
Data Writes
†
Program Writes
Data Reads
‡
Program Reads
‡
Lowest:
Fetches
3.2.3 Peripheral Bus
To enable migration of peripherals between various Texas Instruments (TI) DSP family of devices, the F281x
and C281x adopt a peripheral bus standard for peripheral interconnect. The peripheral bus bridge multiplexes
the various busses that make up the processor “Memory Bus” into a single bus consisting of 16 address lines
and 16 or 32 data lines and associated control signals. Two versions of the peripheral bus are supported on
the F281x and C281x. One version only supports 16-bit accesses (called peripheral frame 2) and this retains
compatibility with C240x-compatible peripherals. The other version supports both 16- and 32-bit accesses
(called peripheral frame 1).
3.2.4 Real-Time JTAG and Analysis
The F281x and C281x implement the standard IEEE 1149.1 JTAG interface. Additionally, the F281x and
C281x support real-time mode of operation whereby the contents of memory, peripheral and register locations
can be modified while the processor is running and executing code and servicing interrupts. The user can also
single step through non-time critical code while enabling time-critical interrupts to be serviced without
interference. The F281x and C281x implement the real-time mode in hardware within the CPU. This is a
unique feature to the F281x and C281x, no software monitor is required. Additionally, special analysis
hardware is provided which allows the user to set hardware breakpoint or data/address watch-points and
generate various user selectable break events when a match occurs.
3.2.5 External Interface (XINTF) (2812 Only)
This asynchronous interface consists of 19 address lines, 16 data lines, and three chip-select lines. The
chip-select lines are mapped to five external zones, Zones 0, 1, 2, 6, and 7. Zones 0 and 1 share a single
chip-select; Zones 6 and 7 also share a single chip-select. Each of the five zones can be programmed with
a different number of wait states, strobe signal setup and hold timing and each zone can be programmed for
extending wait states externally or not. The programmable wait-state, chip-select and programmable strobe
timing enables glueless interface to external memories and peripherals.
†
‡
Simultaneous Data and Program writes cannot occur on the Memory Bus.
Simultaneous Program Reads and Fetches cannot occur on the Memory Bus.
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April 2001 − Revised December 2004
SPRS174L
TI [ TEXAS INSTRUMENTS ]
