SX28ACSLASHDP datasheet(4/51 Pages) PARALLAX

4 / 51 page

Parallax SX20AC/SX28AC

www.parallax.com

Page 4 of 51

Rev 1.6 11/20/2006

1.3.

Architecture

The SX devices use a modified Harvard architecture. This

architecture uses two separate memories with separate

address buses, one for the program and one for data, while

allowing transfer of data from program memory to

SRAM. This ability allows accessing data tables from

program memory. The advantage of this architecture is

that instruction fetch and memory transfers can be

overlapped with a multi-stage pipeline, which means the

next instruction can be fetched from program memory

while the current instruction is being executed using data

from the data memory.

This RISC-like architecture and memory design is based

on technology that makes it very fast, deterministic, jitter

free, and totally reprogrammable.

The SX family implements a four-stage pipeline (fetch,

decode, execute, and write back), which results in

execution of one instruction per clock cycle. For example,

at the maximum operating frequency of 75 MHz,

instructions are executed at the rate of one per 13.3 ns

clock cycle.

1.4.

Programming Benefits in Assembly

and High-Level Languages

The SX’s high speed enables a “software system on a

chip” approach. Programming in assembly language

provides a particularly high-level of access to the interrupt

service routine, the stack and registers to take the highest

advantage of the SX’s deterministic timing. The primary

technical resources for programming the SX in assembly

language include the following:

• The SX20AC/SX28AC datasheet

• SX-Key Development System User’s Manual by

Parallax, Inc.

• Programming the SX Microcontroller – A Complete

Guide by Guenther Daubach

Customers with a high-level programming language

background may prefer the use of a C or BASIC

compiler.

1.4.1. Parallax SX/B Basic Compiler

Parallax's SX/B is a free BASIC language compiler for

the SX microcontroller (SX20, SX28, and SX48). The

compiler

speeds

the

programming

the

microcontrollers by providing a simple, yet robust high-

level language familiar to Parallax customers. SX/B

includes the following features and commands:

• ASM directive to support in-line assembly language

• Program structure commands including BRANCH,

DO..LOOP, GOTO, GOSUB, IF..THEN..ELSE

• Numeric formatters

• WORD variable support

• Frequency generation with FREQOUT

• Synchronous serial communication for I

2C, 1-Wire,

SPI

• Asynchronous serial communication with SERIN

and SEROUT

• Table data storage and retrieval with LOOKUP,

LOOKDOWN

• I/O pin control with HIGH, LOW, TOGGLE,

REVERSE

• Timing and delay with PAUSE, SLEEP

• PULSIN and PULSOUT

• Resistor/capacitor A/D with RCTIME

• RANDOM for pseudo-random number generation

• Non-volatile EEPROM memory access with DATA,

READ

• Low-current SLEEP command

The complete SX/B command reference and examples are

installed with the SX-Key IDE.

1.5.

Programming and Debugging

Support

The SX devices are supported by Parallax’s programming

and debugging tools. The Parallax SX-Blitz is a

programming tool. The SX-Key supports programming

and source-level debugging. On-chip in-system debug

capabilities allow the Parallax tool to be an all-in-one

integrated development environment with editor, macro

assembler, debugger, and programmer. Unobtrusive in-

system programming is provided through the OSC pins.

Visit www.parallax.com for the SX-Key development

tools, the IDE and support forum information.

The in-system programming specification is available to

other 3rd party tool vendors upon request.

1.6.

Applications

The SX may be used as a solution for process controllers,

electronic appliances/tools, security/monitoring systems,

sound and signal generation, GPS interface, robotic

control, motor control, sensor interfacing and personal

communication devices. Applications such as interactive

toys, magnetic-stripe readers, infrared decoders, and other

timing-sensitive projects are also common with the SX.

Examples of customer applications may be seen on the

Parallax web site.

1.7.

Support

Parallax and our distributors provide all support for the

SX microcontroller. Support is available free of charge

via phone (888) 512-1024 in the U.S. Also be sure to

participate

the

discussion

forum

http://forums.parallax.com/forums/.

The

on-line

support community is actively involved in customer

support 24 hours a day.

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