p8x32a Parallax, Inc., p8x32a Datasheet - Page 6

• Manufacturer Part Number: p8x32a
• Description: 8-cog Multiprocessor Microcontroller
• Manufacturer: Parallax, Inc.

Propeller™ P8X32A Datasheet
3.0
3.1.
Upon power-up, or reset:
1. The Propeller chip’s internal RC oscillator begins
2. The Boot Loader performs one or more of the
3. If either step 2a or 2b was successful in loading a
3.2.
A Propeller Application is a user program compiled into
its binary form and downloaded to the Propeller chip’s
RAM or external EEPROM. The application consists of
code written in the Propeller chip’s Spin language (high-
level code) with optional Propeller Assembly language
components (low-level code). Code written in the Spin
language is interpreted during run time by a cog running
the Spin Interpreter while code written in Propeller
Assembly is run in its pure form directly by a cog. Every
Propeller Application consists of at least a little Spin code
and may actually be written entirely in Spin or with
various amounts of Spin and assembly. The Propeller
chip’s Spin Interpreter is started in Step 3 of the Boot Up
Procedure, above, to get the application running.
Once the boot-up procedure is complete and an
application is running in Cog 0, all further activity is
defined by the application itself. The application has
complete control over things like the internal clock speed,
Copyright © Parallax Inc.
running at 20 kHz, then after a 50 ms reset delay,
switches to 12 MHz. Then the first processor (Cog 0)
loads and runs the built-in Boot Loader program.
following tasks, in order:
a.
b. If no host communication was detected, the Boot
c.
program into the global RAM, and a suspend
command was not given by the host, then Cog 0 is
reloaded with the built-in Spin Interpreter and the
user code is run from global RAM.
OPERATING PROCEDURES
Boot-Up Procedure
Detects communication from a host, such as a
PC, on pins P30 and P31. If communication
from a host is detected, the Boot Loader
converses with the host to identify the Propeller
chip and possibly download a program into
global RAM and optionally into an external 32
KB EEPROM.
Loader looks for an external 32 KB EEPROM on
pins P28 and P29. If an EEPROM is detected,
the entire 32 KB data image is loaded into the
Propeller chip’s global RAM.
If no EEPROM was detected, the boot loader
stops, Cog 0 is terminated, the Propeller chip
goes into shutdown mode, and all I/O pins are set
to inputs.
Run-Time Procedure
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I/O pin usage, configuration registers, and when, what
and how many cogs are running at any given time. All of
this is variable at run time, as controlled by the
application.
3.3.
When the Propeller goes into shutdown mode, the internal
clock is stopped causing all cogs to halt and all I/O pins
are set to input direction (high impedance). Shutdown
mode is triggered by one of the three following events:
1. VDD falling below the brown-out threshold (~2.7
2. the RESn pin going low, or
3. the application requests a reboot (see the REBOOT
Shutdown mode is discontinued when the voltage level
rises above the brown-out threshold and the RESn pin is
high.
4.0
4.1.
There are two types of shared resources in the Propeller:
1) common, and 2) mutually-exclusive.
resources can be accessed at any time by any number of
cogs. Mutually-exclusive resources can also be accessed
by any number of cogs, but only by one cog at a time.
The common resources are the I/O pins and the System
Counter.
exclusive by nature and access to them is controlled by
the Hub. See Section 4.4 on page 7.
4.2.
The System Clock (shown as “CLOCK” in Figure 1, page
1) is the central clock source for nearly every component
of the Propeller chip. The System Clock’s signal comes
from one of three possible sources:
The source is determined by the CLK register’s settings,
which is selectable at compile time and reselectable at run
time.
System Clock speed.
• The internal RC oscillator (~12 MHz or ~20 kHz)
• The XI input pin (either functioning as a high-
• The Clock PLL (phase-locked loop) fed by the XI
VDC), when the brown out circuit is enabled,
command in the Propeller Manual).
impedance
conjunction with the XO pin)
input
The Hub and internal Bus operate at half the
Shutdown Procedure
SYSTEM ORGANIZATION
Shared Resources
System Clock
All other shared resources are mutually-
input
or
a
crystal
Rev 1.0 11/14/2007
www.parallax.com
oscillator
Common
in