AM29240EH AMD [Advanced Micro Devices], AM29240EH Datasheet - Page 9

• Manufacturer Part Number: AM29240EH
• Description: Enhanced High-Performance RISC Microcontrollers
• Manufacturer: AMD [Advanced Micro Devices]

Software debugging is facilitated by the instruction
trace facility and instruction breakpoints. Instruction
tracing is accomplished by forcing the processor to trap
after each instruction has been executed. Instruction
breakpoints are implemented by the HALT instruction
or by a software trap.
The processor provides several additional features to
assist system debugging and testing:
PERFORMANCE OVERVIEW
The Am29240EH microcontroller series offers a signifi-
cant margin of performance over CISC microprocessors
in existing embedded designs, since the majority of pro-
cessor features were defined for the maximum achiev-
able performance at very low cost. This section
describes the features of the Am29240EH microcontrol-
ler series from the point of view of system performance.
Instruction Timing
The Am29240EH microcontroller series uses an arith-
metic/logic unit, a field shift unit, and a prioritizer to
execute most instructions. Each of these is organized to
operate on 32-bit operands and provide a 32-bit result.
All operations are performed in a single cycle.
The performance degradation of load and store opera-
tions is minimized in the Am29240EH microcontroller
series by overlapping them with instruction execution,
by taking advantage of pipelining, by an on-chip data
cache, and by organizing the flow of external data into
the processor so that the impact of external accesses is
minimized.
Pipelining
Instruction operations are overlapped with instruction
fetch, instruction decode and operand fetch, instruction
execution, and result write-back to the Register File.
Pipeline forwarding logic detects pipeline dependencies
and routes data as required, avoiding delays that might
arise from these dependencies. Pipeline interlocks are
implemented by processor hardware. Except for a few
The Test/Development Interface is composed of a
group of pins that indicate the state of the processor
and control the operation of the processor.
A Traceable Cache feature permits a hardware-
development system to track accesses to the on-
chip caches, permitting a high level of visibility into
processor operation.
An IEEE Std 1149.1-1990 (JTAG) compliant Stan-
dard Test Access Port and Boundary-Scan Architec-
ture. The Test Access Port provides a scan interface
for testing processor and system hardware in a pro-
duction environment, and contains extensions that
allow a hardware-development system to control
and observe the processor without interposing hard-
ware between the processor and system.
Am29240 EH Microcontroller Series
P R E L I M I N A R Y
special cases, it is not necessary to rearrange programs
to avoid pipeline dependencies, although this is some-
times desirable for performance.
On-Chip Instruction and Data Caches
On-chip instruction and data caches satisfy most proces-
sor fetches without wait states. The caches are pipelined
for best performance. The reload policies minimize the
amount of time spent waiting for reload, while optimizing
the benefit of locality of reference.
Burst-Mode and Page-Mode Memories
The Am29240EH microcontroller series directly sup-
ports burst-mode memories. The burst-mode memory
supplies instructions at the maximum bandwidth, with-
out the complexity of an external cache or the perfor-
mance degradation due to cache misses.
The processor can also use the page-mode capability of
common DRAMs to improve the access time in cases
where page-mode accesses can be used.
Instruction Set Overview
All 29K family members employ a three-address instruc-
tion set architecture. The compiler or assembly-lan-
guage programmer is given complete freedom to
allocate register usage. There are 192 general-purpose
registers, allowing the retention of intermediate calcula-
tions and avoiding needless data destruction. Instruc-
tion operands may be contained in any of the
general-purpose registers, and the results may be
stored into any of the general-purpose registers.
The Am29240EH microcontroller series instruction set
contains 117 instructions that are divided into nine
classes. These classes are integer arithmetic, compare,
logical, shift, data movement, constant, floating point,
branch, and miscellaneous. The floating-point instruc-
tions are not executed directly, but are emulated by trap
handlers.
All directly implemented instructions are capable of
executing in one processor cycle, with the exception of
interrupt returns, loads, and stores.
Data Formats
The Am29240EH microcontroller series defines a word
as 32 bits of data, a half-word as 16 bits, and a byte as 8
bits. The hardware provides direct support for word-
integer (signed and unsigned), word-logical, word-Bool-
ean, half-word integer (signed and unsigned), and char-
acter data (signed and unsigned).
Word-Boolean data is based on the value contained in
the most significant bit of the word. The values TRUE
and FALSE are represented by the most significant bit
values 1 and 0, respectively.
Other data formats, such as character strings, are sup-
ported by instruction sequences. Floating-point formats
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